Aquarium Chemistry Question? Ask the Doctor!

[Sgchick]

Hi Randy, I just bought a new Salifert Alkalinity test kit and noticed the directions have changed. The old kit said to add 4 drops to your tank water (4ml) and 2 drops for low resolution. The new kit says to add 2 drops and (1 drop) for low resolution. Did I get some bad instructions? Not sure how to find out ...Thanks, Melanie

 

[Scott.h]

You should not dose it in amounts to raise pH. Alkalinity is the driving concern,a nd it is an alkalinity supplement. Use it to boost alkalinity when needed, and you get whatever pH boost is there. But you should not ever determine the amount to use to figure a pH boost.

That said, for each 1.4 dKH of alkalinity added, it will immediately, and perhaps temporarily, boost pH by about 0.35 pH units.

These discussions explain what these parameters represent:

https://www.reef2reef.com/threads/o...-reef-aquarium-by-randy-holmes-farley.173563/

Alkalinity

Like calcium, many corals also use "alkalinity" to form their skeletons, which are composed primarily of calcium carbonate. It is generally believed that corals take up bicarbonate, convert it into carbonate, and then use that carbonate to form calcium carbonate skeletons. That conversion process is shown as:

HCO3- → CO3-- + H+

Bicarbonate → Carbonate + proton (which is released from the coral)

To ensure that corals have an adequate supply of bicarbonate for calcification, aquarists could just measure bicarbonate directly. Designing a test kit for bicarbonate, however, is somewhat more complicated than for alkalinity. Consequently, the use of alkalinity as a surrogate measure for bicarbonate is deeply entrenched in the reef aquarium hobby.

So, what is alkalinity? Alkalinity in a marine aquarium is simply a measure of the amount of acid (H+) required to reduce the pH to about 4.5, where all bicarbonate is converted into carbonic acid as follows:

HCO3- + H+ → H2CO3

The amount of acid needed is equal to the amount of bicarbonate present, so when performing an alkalinity titration with a test kit, you are “counting†the number of bicarbonate ions present. It is not, however, quite that simple since some other ions also take up acid during the titration. Both borate and carbonate also contribute to the measurement of alkalinity, but the bicarbonate dominates these other ions since they are generally lower in concentration than bicarbonate. So knowing the total alkalinity is akin to, but not exactly the same as, knowing how much bicarbonate is available to corals. In any case, total alkalinity is the standard that aquarists use for this purpose.

Unlike the calcium concentration, it is widely believed that certain organisms calcify more quickly at alkalinity levels higher than those in normal seawater. This result has also been demonstrated in the scientific literature, which has shown that adding bicarbonate to seawater increases the rate of calcification in some corals. Uptake of bicarbonate can consequently become rate limiting in many corals. This may be partly due to the fact that the external bicarbonate concentration is not large to begin with (relative to, for example, the calcium concentration, which is effectively about 5 times higher).

For these reasons, alkalinity maintenance is a critical aspect of coral reef aquarium husbandry. In the absence of supplementation, alkalinity will rapidly drop as corals use up much of what is present in seawater. Water changes are not usually sufficient to maintain alkalinity unless there is very little calcification taking place. Most reef aquarists try to maintain alkalinity at levels at or slightly above those of normal seawater, although exactly what levels different aquarists target depends a bit on the goals of their aquaria.

Interestingly, because some corals may calcify faster at higher alkalinity levels, and because the abiotic (nonbiological) precipitation of calcium carbonate on heaters and pumps also rises as alkalinity rises, the demand for alkalinity (and calcium) rises as the alkalinity rises. So an aquarist generally must dose more calcium and alkalinity EVERY DAY to maintain a higher alkalinity (say, 11 dKH) than to maintain 7 dKH. It is not just a one-time boost that is needed to make up that difference. In fact, calcification gets so slow as the alkalinity drops below 6 dKH that reef aquaria rarely get much below that point, even with no dosing: natural calcification has nearly stopped at that level.

In general, I suggest that aquarists maintain alkalinity between about 7-11 dKH (2.5 and 4 meq/L; 125-200 ppm CaCO3 equivalents). Many aquarists growing SPS corals and using Ultra Low Nutrient Systems (ULNS) have found that the corals suffer from “burnt tips†if the alkalinity is too high or changes too much. It is not at all clear why this is the case, but such aquaria are better served by alkalinity in the 7-8 dKH range.
As mentioned above, alkalinity levels above those in natural seawater increase the abiotic precipitation of calcium carbonate on warm objects such as heaters and pump impellers, or sometimes even in sand beds. This precipitation not only wastes calcium and alkalinity that aquarists are carefully adding, but it also increases equipment maintenance requirements and can “damage†a sand bed, hardening it into a chunk of limestone. When elevated alkalinity is driving this precipitation, it can also depress the calcium level. An excessively high alkalinity level can therefore create undesirable consequences.

I suggest that aquarists use a balanced calcium and alkalinity additive system of some sort for routine maintenance. The most popular of these balanced methods include limewater (kalkwasser), calcium carbonate/carbon dioxide reactors, and the two-part/three part additive systems.

For rapid alkalinity corrections, aquarists can simply use baking soda (sodium bicarbonate) or washing soda (sodium carbonate; baked baking soda) to good effect. The latter raises pH as well as alkalinity while the former has a very small pH lowering effect. Mixtures can also be used, and are what many hobby chemical supply companies sell as “buffersâ€. Most often, sodium carbonate is preferred, however, since most tanks can be helped by a pH boost.

pH

pH is a measure of the concentration of protons (H+ ions) and hydroxide (OH-) ions in the water. Aquarists spend a considerable amount of time and effort worrying about, and attempting to solve, apparent problems with the pH of their aquaria. Some of this effort is justified, as true pH problems can lead to poor animal health. In many cases, however, the only problem is with the pH measurement or its interpretation. Moreover, the maintenance of appropriate alkalinity in seawater goes a long way to ensuring that the pH is acceptable, with just a couple of exceptions that will be discussed below.

Several factors make monitoring a marine aquarium's pH level useful. One is that aquatic organisms thrive only in a particular pH range, which varies from organism to organism. It is therefore difficult to justify a claim that a particular pH range is "optimal" in an aquarium housing many species. Even natural seawater's pH (8.0 to 8.3) may be suboptimal for some of its creatures, but it was recognized more than eighty years ago that pH levels different from natural seawater (down to 7.3, for example) are stressful to fish. Additional information now exists about optimal pH ranges for many organisms, but the data are inadequate to allow aquarists to optimize pH for most organisms which interest them.

Additionally, pH's effect on organisms can be direct, or indirect. The toxicity of metals such as copper and nickel to some aquarium organisms, such as mysids and amphipods, is known to vary with pH. Consequently the acceptable pH range of one aquarium may differ from another aquarium, even if they contain the same organisms, but have different concentrations of metals.

Changes in pH nevertheless do substantially impact some fundamental processes taking place in many marine organisms. One of these fundamental processes is calcification, or deposition of calcium carbonate skeletons, which is known to depend on pH, usually dropping as pH falls. At a low enough pH (somewhere below pH 7.7) coral skeletons can begin to slowly dissolve. Using this type of information, along with the integrated experience of many hobbyists, we can develop some guidelines about what is an acceptable pH range for reef aquaria, and what values push the limits.

The acceptable pH range for reef aquaria is an opinion rather than a clear fact, and will certainly vary with the opinion's provider. This range may also be quite different from the "optimal" range. Justifying what is optimal, however, is much more problematic than is justifying that which is simply acceptable, so we will focus on the latter. As a goal, I'd suggest that the pH of natural seawater, about 8.2, is appropriate, but coral reef aquaria can clearly succeed in a wider range of pH values. In my opinion, the pH range from 7.8 to 8.5 is an acceptable range for reef aquaria.

In truth, many aquarists never measure pH, and many that do so do not do anything with the results they obtain. This lack of action is usually okay, as most aquaria do not naturally fall outside of the acceptable ranges. Times when it is most important to at least check pH once in a while are:

1. When using very high pH additives, such as limewater (kalkwasser). In this case, one should ensure that the pH does not get above about 8.55. At higher values, the precipitation of calcium carbonate on pumps and such can become excessive. Every 0.3 pH unit rise in pH is equivalent to about a doubling of the calcium or alkalinity value in terms of the likelihood of precipitation of calcium carbonate (because bicarbonate turns into carbonate as the pH rises, driving precipitation). Aquaria may often get to a pH that is high enough to double the precipitation rate due to elevated pH, but one does not often see aquaria with calcium or alkalinity that is double the normal value, making high pH a big driver of precipitation.

2. When the air around the aquarium has elevated carbon dioxide levels, such as in a newer, tighter home. Low pH due to elevated carbon dioxide in the air is VERY common. While it may be useful to ensure the pH stays above 8.0, there are many fine aquaria with the bottom end of the pH range at pH 7.8. Below that value, I'd want to take more aggressive action, such as more fresh air in the home, top off with limewater (kalkwasser), a fresh air line from outside to a skimmer inlet, or a CO2 scrubber on a skimmer inlet.

Referring to the ph, what makes 7.8 concidered to be the low point? What is happening at 7.7 or below to make coral skeletons dissolve? The lower the ph does that make the oxygen levels lower in the water as well?

 

[Randy Holmes-Farley]

Referring to the ph, what makes 7.8 concidered to be the low point? What is happening at 7.7 or below to make coral skeletons dissolve? The lower the ph does that make the oxygen levels lower in the water as well?

pH is independent of O2.

The exact pH at which calcium carbonate is exactly saturated (dissolves at lower pH, precipitates at higher pH) depends on the alkalinity (the carbonate concentration, specifically) and the calcium level. Higher alk (carbonate) and higher calcium raise the saturation pH.

A doubling of either (alk from 7 to 14 dKH or calcium from 420 to 840 ppm) will move the pH of saturation up by 0.3 pH units. It also depends a little bit on temp and salinity (and even pressure in the very deep ocean).

geeky math below....

The saturation state is actually determined by:

(2) Ksp* = [Ca++] x [CO3--] (saturation)
(3) Ksp* < [Ca++] x [CO3--] (supersaturation)
(4) Ksp* > [Ca++] x [CO3--] (undersaturation)
where Ksp* has an exact, known value, [Ca++] is the calcium concentration, and [CO3--] is the carbonate concentration

this is discussed more here:
Chemistry and the Aquarium: Calcium ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/2002/3/chemistry

In exactly normal NSW at about pH 8.2, the water is slightly supersaturated by a factor of about 3 relative to aragonite dissolution and precipitation. That is, the product [Ca++] x [CO3--] is 3* the Ksp*

Each drop in pH of 0.3 pH units corresponds to a decrease in carbonate concentration by about half (as it is converted into bicarbonate). So a drop of 0.3 pH units is a drop in carbonate by half, and hence a reduction in saturation/supersaturation by half. A drop of 0.6 pH untis is two drops by hal, or a drop to 25% of the previous carbonate level.

In order to lower the supersaturation (Ksp*) to exactly 1 from 3 (meaning it is exactly at its solubility limit), a pH drop of about 0.48 pH units is required. That drop lowers the carbonate by about a factor of 3.

So a drop of 0.47 pH units from a starting point of 8.2 gives us a pH of about 7.7.

 

[Randy Holmes-Farley]

Hi Randy, I just bought a new Salifert Alkalinity test kit and noticed the directions have changed. The old kit said to add 4 drops to your tank water (4ml) and 2 drops for low resolution. The new kit says to add 2 drops and (1 drop) for low resolution. Did I get some bad instructions? Not sure how to find out ...Thanks, Melanie

The amount of colorant added is not important to the test, as long as you can distinguish the colors.

 

[Sgchick]

The amount of colorant added is not important to the test, as long as you can distinguish the colors.

Perfect!! Thanks Randy!

 

[Randy Holmes-Farley]

Perfect!! Thanks Randy!

You're welcome.

Happy reefing.

 

[Scott.h]

My concern with drinking RO water is bacterial contamination downstream of where the carbon filter removes any disinfectant. If they regularly sanitize the system, then it may be OK.

My concern with using Ro water is that it may have a lot of ammonia in it (if your tap water has chloramine) and silicate (often present naturally or added to boost pH to reduce copper and lead release from pipes). Generally, I do not recommend using RO only water, and TDS is not a great gauge of what is in it.

What would be the difference in worrying about bacteria in RO/DI vs someone that has a well pumping water out of the ground? There are no chemicals in well water to prevent bacteria growth. We don't clean out/sterilize pipes in our house. Wouldn't that be the same scenario?

 

[Randy Holmes-Farley]

What would be the difference in worrying about bacteria in RO/DI vs someone that has a well pumping water out of the ground? There are no chemicals in well water to prevent bacteria growth. We don't clean out/sterilize pipes in our house. Wouldn't that be the same scenario?

Probably. Well issues might be worse since it might be a friendlier environment to bacteria than the really low ionic strength RO/DI.

 

[zieg9479]

Randy, Any idea what's going on here?
A few months ago I threw in a bag of API activated carbon. I hadn't tried it before and wanted to see if it would benefit my tank. Well, I couldn't decipher a difference but I had also forgotten about the bag in the sump.
I also run n/p pellets and decided to look at that today. I saw I had a bag of carbon in there and pulled it open knowing it was likely spent and full of DOCs.

Anyway for those curious here is the visual result. There is the original carbon, and smaller brown, rusty particles. I have no idea what the orange roe looking pellets are. The casing is hard but they can be smushed. The only livestock I have down there is an emerald crab, macroalgae, and hitchhiker porcelain crabs.
Are the casings DOCs and why do I see what looks like rust from activated carbon (It smeared like rust)? Impurities? Does this mean I am getting some GFO-like benefit?

 

[Randy Holmes-Farley]

You never used any GFO? It looks to me like a mix of GFO and GAC, plus the round beads of undetermined nature.

Do you recall the exact API product? They have some that are mixtures of activated carbon and other things (e.g., AMMO-CARB)

The beads might be a DI resin?

Overall, the mix of things looks possibly like ChemiPure Elite, which has GAC, GFO, and DI resin all together. Any chance you used that?

 

[zieg9479]

hmm maybe I did have chemi pure in my sump...

 

[Randy Holmes-Farley]

If possible, that's the most likely explanation.

 

[Danny Venditti]

Randy,

I switched from Aquaforest 1,2,3, to B-Ionic 2 part. Will it be necessary to dose extra Mg to maintain the level at 1350 or does the 2 part contain enough?

 

[Randy Holmes-Farley]

Randy,

I switched from Aquaforest 1,2,3, to B-Ionic 2 part. Will it be necessary to dose extra Mg to maintain the level at 1350 or does the 2 part contain enough?

B-ionic should maintain it, at least for a substantial period. I'm not sure how much consumption of Mg they assumed.

 

[Danny Venditti]

B-ionic should maintain it, at least for a substantial period. I'm not sure how much consumption of Mg they assumed.

I bought a bottle of ESV Mag anyway just in case but haven't used it yet.

Also what would cause Ca to remain the same over several days with no dose. Corals seem fine but Ca has not moved at all for 4 days?

 

[Danny Venditti]

I bought a bottle of ESV Mag anyway just in case but haven't used it yet.

Also what would cause Ca to remain the same over several days with no dose. Corals seem fine but Ca has not moved at all for 4 days?

Mg @ 1350 and ALK is 8.3

 

[Randy Holmes-Farley]

I bought a bottle of ESV Mag anyway just in case but haven't used it yet.

Also what would cause Ca to remain the same over several days with no dose. Corals seem fine but Ca has not moved at all for 4 days?

How much did alk decline?

If you lost 1 dKH per day, you might hardly see the calcium decline, since it is only about 6-7 ppm per day.

 

[Danny Venditti]

How much did alk decline?

If you lost 1 dKH per day, you might hardly see the calcium decline, since it is only about 6-7 ppm per day.

ok that makes sense. The DKH was 8.0 and I am slowly bringing it up after a 15% water change (Tin came up on recent test) I think it just probably needs time to adjust to the change and new dosing.

 

[Danny Venditti]

ok that makes sense. The DKH was 8.0 and I am slowly bringing it up after a 15% water change (Tin came up on recent test) I think it just probably needs time to adjust to the change and new dosing.

so Randy, what is your opinion on dosing frequency

1. A little several times a day
2. More each time and less times a day but spread out.
3. Same as 2 but close together
4. all at once and only once a day
5. it doesn't matter/

 

[chomoney]

Randy -

What are the potential downfalls are high potassium levels in a reef tank? Also, if there are negative effects, what level would you consider “too high?”

Thanks!