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Water Changes. Benefits and Caveats
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One of the main challenges facing any reef aquarium hobbyist is the maintenance of water chemistry conditions within recommended ranges. This maintenance involves the removal or reduction of detrimental compounds (e.g., excess phosphates and nitrates, biological toxins, etc.) along with the replenishment of other beneficial consumed elements (e.g., calcium, magnesium or trace elements).
For the removal of excess nutrients, both organic and inorganic, there are numerous techniques available, for example, skimmers, activated carbon or GFO. For the replenishment of calcium, magnesium and alkalinity, the balling system or calcium reactors are good options, among others. We can say that nowadays the hobbyist has at his disposal an extensive menu of valid and proven options to maintain optimal water quality in his aquarium.
Water changes are one of these techniques, namely rapid export, probably the oldest due to its simplicity , since they do not require any complicated technological process, nor sophisticated equipment in manual mode. In its simplest version, the make-up water should try to maintain the same chemical parameters as the existing water in the tank: ionic concentrations, salinity, alkalinity, pH and temperature.
Benefit of water changes
- The most significant benefit is undoubtedly the removal of nitrate and phosphate in excess from the aquarium water, in a percentage equal to the ratio between the partial volume exchanged and the total net volume of the aquarium, including the sump. The change involves an abrupt decrease in these concentrations and those of other existing compounds not contained in the exchanged saltwater, according to this ratio.
- Removal of biological toxins, waste products of biological activity and harmful compounds that mechanical or chemical filtration (skimmer, fleece, activated carbon) has not previously been able to remove for any reason, e.g., refractory organic substances such as phenols.
- Removal of unintentionally introduced contaminants, e.g., excess trace elements, copper, aluminum and other toxic metals in excess.
- Contribution to the restoration of ionic balance, i.e., the relationship that exists in natural seawater between the concentrations of constituent ions: calcium, magnesium, carbonates, bicarbonate, sulfate, chloride, sodium, strontium or boron, among many others. This is very important when using Balling or unbalanced calcium and alkalinity additives.
- A weekly or monthly routine of water changes keeps you in touch with the aquarium, facilitating the hobbyist's bond of interest and increasing opportunities for observation so that you can anticipate problems before it is too late.
Disadvantages of water changes
As indicated, a water change implies an abrupt reduction in the concentrations of elements in the aquarium that are not part of the natural seawater, for example, nitrate and phosphate in excess. However, we know that for an aquarium to operate stably, within reasonable limits, it is necessary that the concentration of dissolved compounds in the water remains as stable as possible over time. A large volume water change will produce a sudden change that could destabilize the tank. For example, we know that performing water changes in an aquarium with a dinoflagellate infestation will significantly worsen the situation. Similarly, there is some likelihood that the chemical parameters of the new water will not match the existing ones, which can temporarily stress fish, corals and other invertebrates.
Even if the new saltwater has the same salinity and temperature as the aquarium water, there are other parameters that in most cases are different, e.g. pH, redox potential or dissolved oxygen. For example, it is common to see a drop in redox potential, pH and dissolved oxygen in the aquarium after a water change.
The transparency of the water is also changed suddenly after a large volume change. This implies an abrupt increase in light radiation that impacts fish, corals and other invertebrates, which can be detrimental depending on the magnitude of the increase experienced. Therefore, it is good practice to program the lights in acclimation mode prior to a large volume change.
Limitations of water changes
As one of the advantages of water changes is the reduction of nitrate and phosphate concentrations, in principle both equally (with some exceptions that we explain below), this could lead us to think that, by performing water changes of a certain percentage, with a certain periodicity, we could indefinitely maintain the nitrate and phosphate concentrations within the recommended ranges.
The reality is that, in tanks of medium or large volume, and depending on the organic load, water changes are not a sufficient tool to maintain pollution in acceptable values, without relying on other techniques such as mechanical/chemical filtration or denitrification and recycling of nitrate and phosphate by adding organic carbon. The reason is that too much frequently water changes of significant volume are necessary, which is neither practical nor economical. This does not mean that the changes are not beneficial, because they help to remove toxic metals, maintain ionic balance, salinity and trace element replenishment.
To illustrate this, figure 1 shows a simulation of the evolution in time of nitrate concentration (for example), starting at 1 mg/l, in a tank where weekly water changes of certain volume (10% to 50% in the graph) are performed. The scenario assumes an increase of 1.5 mg/l of nitrate per week (from nitrification). We can see that to stabilize a permanent concentration of aprox. 5 ppm, performing a 20% volume change per week, we need around 20 weeks! Figure 2 shows the number of weeks needed to reach stability versus the exchanged water volume per week with same assumptions.
Figure 1. Number of weeks needed to reach stability with water changes (versus % volume)
Figure 2. Weeks needed to reach stability versus % of weekly exchanged water volume.
On the other hand, when an aquarium has a very high phosphate concentration, phosphate precipitation occurs on the aragonite crystals of the live rock, in the form of calcium phosphate. This means that after a water change of for example 50% of the volume, due to phosphate concentration decrease, part of the previously precipitated phosphate will pass back into the water column, and the final concentration will not be half but higher. This phenomenon does not occur with nitrate.
Figure 3 shows a simulation graph of the number of changes required to reduce the concentration of any compound in the aquarium water (in percentages of 90% to 40%), with water changes of partial volume between 10% and 100%. For example, for a 60% nitrate reduction with 30% volume changes, 2.5 changes are required.
Figure 3. Number of changes required versus % volume.
Aquariums without water changes
Although it is possible to successfully maintain reef aquariums without water changes for months or years, it seems that the value of this practice comes more from a personal satisfaction than anything else. These types of aquariums require very detailed monitoring with frequent ICP analysis to verify trace element concentrations, which sometimes the ICP tests themselves are not able to determine with sufficient accuracy. The changes facilitate the maintenance of the ionic balance in a simple way, with replenishment of trace elements without the risk of overdosing, which in some cases can produce a real disaster.
Implementation
New hobbyists entering the hobby wonder how often to perform water changes and what percentage. Obviously, it depends on each situation, but a good practice would be as follows: in the first months of operation, as long as nitrate and phosphate concentrations do not skyrocket, no changes are necessary, as the population of corals and other invertebrates will be small. The absence of water changes helps to stabilize the aquarium, especially during the first months where algae pests are frequent. Subsequently, rather than daily or weekly changes, which imply a greater effort, a monthly change of 10%-20% is recommended. It is well known that the fewer actions we perform in the aquarium, the greater the tranquility of the animals and the lower the probability of occurrence of destabilizing events.
There are many ways to perform the changes, both manual and automatic, using timers, level control or peristaltic pumps for continuous use. A rather convenient way is to stop the return pump and filtration devices, siphon all the contents of the sump and add new water. The return pump is switched on again and that's it. In this way it is not necessary to introduce any tubing into the aquarium, which can stress the fish.
In reference to water changes and other nutrient recycling and exporting techniques, the conclusion is that we should avoid allowing harmful compounds to reach too high concentrations, rather than making abrupt changes afterwards.
For the removal of excess nutrients, both organic and inorganic, there are numerous techniques available, for example, skimmers, activated carbon or GFO. For the replenishment of calcium, magnesium and alkalinity, the balling system or calcium reactors are good options, among others. We can say that nowadays the hobbyist has at his disposal an extensive menu of valid and proven options to maintain optimal water quality in his aquarium.
Water changes are one of these techniques, namely rapid export, probably the oldest due to its simplicity , since they do not require any complicated technological process, nor sophisticated equipment in manual mode. In its simplest version, the make-up water should try to maintain the same chemical parameters as the existing water in the tank: ionic concentrations, salinity, alkalinity, pH and temperature.
Benefit of water changes
- The most significant benefit is undoubtedly the removal of nitrate and phosphate in excess from the aquarium water, in a percentage equal to the ratio between the partial volume exchanged and the total net volume of the aquarium, including the sump. The change involves an abrupt decrease in these concentrations and those of other existing compounds not contained in the exchanged saltwater, according to this ratio.
- Removal of biological toxins, waste products of biological activity and harmful compounds that mechanical or chemical filtration (skimmer, fleece, activated carbon) has not previously been able to remove for any reason, e.g., refractory organic substances such as phenols.
- Removal of unintentionally introduced contaminants, e.g., excess trace elements, copper, aluminum and other toxic metals in excess.
- Contribution to the restoration of ionic balance, i.e., the relationship that exists in natural seawater between the concentrations of constituent ions: calcium, magnesium, carbonates, bicarbonate, sulfate, chloride, sodium, strontium or boron, among many others. This is very important when using Balling or unbalanced calcium and alkalinity additives.
- A weekly or monthly routine of water changes keeps you in touch with the aquarium, facilitating the hobbyist's bond of interest and increasing opportunities for observation so that you can anticipate problems before it is too late.
Disadvantages of water changes
As indicated, a water change implies an abrupt reduction in the concentrations of elements in the aquarium that are not part of the natural seawater, for example, nitrate and phosphate in excess. However, we know that for an aquarium to operate stably, within reasonable limits, it is necessary that the concentration of dissolved compounds in the water remains as stable as possible over time. A large volume water change will produce a sudden change that could destabilize the tank. For example, we know that performing water changes in an aquarium with a dinoflagellate infestation will significantly worsen the situation. Similarly, there is some likelihood that the chemical parameters of the new water will not match the existing ones, which can temporarily stress fish, corals and other invertebrates.
Even if the new saltwater has the same salinity and temperature as the aquarium water, there are other parameters that in most cases are different, e.g. pH, redox potential or dissolved oxygen. For example, it is common to see a drop in redox potential, pH and dissolved oxygen in the aquarium after a water change.
The transparency of the water is also changed suddenly after a large volume change. This implies an abrupt increase in light radiation that impacts fish, corals and other invertebrates, which can be detrimental depending on the magnitude of the increase experienced. Therefore, it is good practice to program the lights in acclimation mode prior to a large volume change.
Limitations of water changes
As one of the advantages of water changes is the reduction of nitrate and phosphate concentrations, in principle both equally (with some exceptions that we explain below), this could lead us to think that, by performing water changes of a certain percentage, with a certain periodicity, we could indefinitely maintain the nitrate and phosphate concentrations within the recommended ranges.
The reality is that, in tanks of medium or large volume, and depending on the organic load, water changes are not a sufficient tool to maintain pollution in acceptable values, without relying on other techniques such as mechanical/chemical filtration or denitrification and recycling of nitrate and phosphate by adding organic carbon. The reason is that too much frequently water changes of significant volume are necessary, which is neither practical nor economical. This does not mean that the changes are not beneficial, because they help to remove toxic metals, maintain ionic balance, salinity and trace element replenishment.
To illustrate this, figure 1 shows a simulation of the evolution in time of nitrate concentration (for example), starting at 1 mg/l, in a tank where weekly water changes of certain volume (10% to 50% in the graph) are performed. The scenario assumes an increase of 1.5 mg/l of nitrate per week (from nitrification). We can see that to stabilize a permanent concentration of aprox. 5 ppm, performing a 20% volume change per week, we need around 20 weeks! Figure 2 shows the number of weeks needed to reach stability versus the exchanged water volume per week with same assumptions.
Figure 1. Number of weeks needed to reach stability with water changes (versus % volume)
Figure 2. Weeks needed to reach stability versus % of weekly exchanged water volume.
On the other hand, when an aquarium has a very high phosphate concentration, phosphate precipitation occurs on the aragonite crystals of the live rock, in the form of calcium phosphate. This means that after a water change of for example 50% of the volume, due to phosphate concentration decrease, part of the previously precipitated phosphate will pass back into the water column, and the final concentration will not be half but higher. This phenomenon does not occur with nitrate.
Figure 3 shows a simulation graph of the number of changes required to reduce the concentration of any compound in the aquarium water (in percentages of 90% to 40%), with water changes of partial volume between 10% and 100%. For example, for a 60% nitrate reduction with 30% volume changes, 2.5 changes are required.
Figure 3. Number of changes required versus % volume.
Aquariums without water changes
Although it is possible to successfully maintain reef aquariums without water changes for months or years, it seems that the value of this practice comes more from a personal satisfaction than anything else. These types of aquariums require very detailed monitoring with frequent ICP analysis to verify trace element concentrations, which sometimes the ICP tests themselves are not able to determine with sufficient accuracy. The changes facilitate the maintenance of the ionic balance in a simple way, with replenishment of trace elements without the risk of overdosing, which in some cases can produce a real disaster.
Implementation
New hobbyists entering the hobby wonder how often to perform water changes and what percentage. Obviously, it depends on each situation, but a good practice would be as follows: in the first months of operation, as long as nitrate and phosphate concentrations do not skyrocket, no changes are necessary, as the population of corals and other invertebrates will be small. The absence of water changes helps to stabilize the aquarium, especially during the first months where algae pests are frequent. Subsequently, rather than daily or weekly changes, which imply a greater effort, a monthly change of 10%-20% is recommended. It is well known that the fewer actions we perform in the aquarium, the greater the tranquility of the animals and the lower the probability of occurrence of destabilizing events.
There are many ways to perform the changes, both manual and automatic, using timers, level control or peristaltic pumps for continuous use. A rather convenient way is to stop the return pump and filtration devices, siphon all the contents of the sump and add new water. The return pump is switched on again and that's it. In this way it is not necessary to introduce any tubing into the aquarium, which can stress the fish.
In reference to water changes and other nutrient recycling and exporting techniques, the conclusion is that we should avoid allowing harmful compounds to reach too high concentrations, rather than making abrupt changes afterwards.
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great job!!!! We all benefit from this
……Skipping water changes works until it doesn’t
……Skipping water changes works until it doesn’t
vlangel
Seahorse whisperer
As the aquarium tech for a successful lfs in my area, I saw how consistent water changes could keep an aquarium functioning beautifully for years and even decades. I have been in the hobby since the late 90s but that had such a profound impact on me that I have always implemented a water change regiment into the care of my own tanks. I do believe that smaller weekly water changes reduces the risk of upsetting the stability of a reef tank and that was how I took care of my tank until recently. Since my own tank is mature at over 7 years old and heavily planted with macroalgae and has dense rock and a deep sand bed for denitrification, I have reduced the frequency of the water changes. That is due to the fact that the bulk of nitrates and Phosphates are being removed biologically. I will not be ceasing with water changes completely as I want to remove toxins and other excess compounds that are not utilized by the macroalgae. Water changes also replenish calcium, alkalinity, iron and iodine plus other stuff which even in my predominantly softie reef are still important. Yes I could dose those elements and others but a water change is easier and less tedious to me than testing. So there you have it, I am a believer in water changes.
Subsea
5000 Club Member
Dawn
Kudoes to you, with mature tanks full of filter feeding inverts and ornamental/utilitarian macro algaes, it is easy to operate with little water changes. Your system biochemistry self regulates with you as the Enviromental Steward. While I don’t schedule water changes on 25 year young display, I vacuum sand with water from tank.
Once a year, I do four 25% water changes in one month to get system back to ocean standards
Most tank inhabitants in my systems come from Gulf of Mexico/Florida Keys. They are robust with much adaptability.
@Beuchat said
Aquariums without water changes
“Although it is possible to successfully maintain reef aquariums without water changes for months or years, it seems that the value of this practice comes more from a personal satisfaction than anything else. These types of aquariums require very detailed monitoring with frequent ICP analysis to verify trace element concentrations, which sometimes the ICP tests themselves are not able to determine with sufficient accuracy. The changes facilitate the maintenance of the ionic balance in a simple way, with replenishment of trace elements without the risk of overdosing, which in some cases can produce a real disaster.“
Bravo! You hit the nail on the head. I see personal satisfaction with matching ecosystem biochemistry with the correct inhabitants. Except I don’t detail monitor with ICP. I have unopened API kits with expired expiration dates, if I need to test.
PS. Actually, if I need to test I send to regional agriculture lab.
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Subsea
5000 Club Member
@Beuchat said
“These types of aquariums require very detailed monitoring“
I say,
Consider that while I don’t embrace water changes that does not disqualify from being an enviromental steward for marine life. Instead of testing to determine environmental conditions, I observe bioindicators of “life in the tank”. This morning while enjoying second cup of coffee, I noted Caulerpa Paspoides indicating “going sexual” with browning of fronds indicating to me, nitrogen limiting. I did two things: I dosed 20 ml of nh3 and I pruned Caulerpa removing ugly part. I feel that agrees with your conclusion paragraph
Benefits of Water Change section.
“weekly or monthly routine of water changes keeps you in touch with the aquarium, facilitating the hobbyist's bond of interest and increasing opportunities for observation so that you can anticipate problems before it is too late.”
“These types of aquariums require very detailed monitoring“
I say,
Consider that while I don’t embrace water changes that does not disqualify from being an enviromental steward for marine life. Instead of testing to determine environmental conditions, I observe bioindicators of “life in the tank”. This morning while enjoying second cup of coffee, I noted Caulerpa Paspoides indicating “going sexual” with browning of fronds indicating to me, nitrogen limiting. I did two things: I dosed 20 ml of nh3 and I pruned Caulerpa removing ugly part. I feel that agrees with your conclusion paragraph
Benefits of Water Change section.
“weekly or monthly routine of water changes keeps you in touch with the aquarium, facilitating the hobbyist's bond of interest and increasing opportunities for observation so that you can anticipate problems before it is too late.”
MnFish1
10K Club member
Not necessarily, unless you're talking about a tank with out of whack parameters and a large volume change. Though many things stay extremely stable in the ocean there are also times where extreme changes can happen. upwellings, typhoons, etc.
I do not think this is proven. Dinoflagellate infestation is probably multifactorial.
It is interesting that even with 20% water changes/week, you can achieve a stable nitrate of 5 (which is fine IMHO) - most tanks benefit from other nitrate removal methods as well as you say. Actually, if you start your water changes immediately, the nitrate will stabalize at 5 eventually (starting near 0). Again - the issue you're mentioning would play a role if someone did water changes starting with lets say a nitrate of 50.
But the graph and point you make is extremely valuable - and something many people do not understand (for example - "Reefer xxxx overdosed copper, and it didn't drop after a 10% water change). There is another website that has calculators that one can input their own values into and make these graphs - I don't know if you used that as a source (Hamzareef.com)
Overall your article was excellent/outstanding in my opinion. Well written and thorough/complete. I might have added more references for some of the comments.
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