how complex is it to calculate the evaporation rate of a typical medium size reef tank?

[Ballyhoo]

I was trying to calculate just generally what the evaporation rate is of my 42 gallon reef tank not considering it's 10 gallon sump which is in the cabinet. I use ChatGPT4 and put in the factors of room temperature 70°, humidity level 50% and water temperature of 81° and ChatGPT4 basically gave me nothing. I'm just wondering if I have 41 gallons of 81° water cubed tank how much generally should I expect evaporate in a day? one gallon.gallon . 1 litte? There's gotta be a ballpark figure at least . I understand. We also have to figure in the surface area of the water. Mine is a cube about 23 x 22". Any ideas just roughly about how much water I might be a evaporating in a 24 hour period? I know there's no way to come up with a concrete answer without doing a mathematical equation, particularly involving surface area of water and maybe surface temperature of water. what else is there? thank you.
edit, I think it's fair to say that if somebody has a reef tank that's 81°, and they live in a typical home with out significant humidity inside the house and you're in 70° room temperature that that water is gonna evaporate pretty quickly? Especially the differential between the warm water and the much cooler air. Not to mention the circulating water from the pumps and reef waves.

 

[JNalley]

It depends on how humid the air already is... Even ballparking is difficult.... Dry air will suck out more water than already humid air because of saturation point... Also, glass or solid lids will slow evaporation. Surface area also plays a role, so a wide low tank will evaporate more than a narrow high tank.

 

[Pistondog]

Very dependent on air velocity at water surface. A fan cools water by increasing the evap rate.
Fwiw, brs estimates 1/2 gallon per day for a 40 gallon tank.

Get saltwater tank evaporation right! This is how it's done and it is VERY easy.

Your reef tank is going to evaporate water, something you can see with the naked eye as the water level drops. What you don’t see is as the water leaves the tank, the salt and other dissolved elements stay behind. That causes the water in your tank to become more concentrated

www.bulkreefsupply.com

 

[VintageReefer]

This is being over complicated for inaccurate results that are a guess at best.

Make a line in the sump with tape

Label date and time

Come back 24 hours and see if the water is lower. Take measuring cup and add water and see what’s needed to bring back to the line. That is your evap for 24 hours.

If not much loss noticeable in 1 day then wait 2 or 3 days and divide the water added by number of days

 

[VintageReefer]

Or get an ATO and 1g container and see how many days before it’s empty

 

[KStatefan]

so many variables it would be very complicated to calculate and then that would just be at one point.

measuring actual would be the easiest way

The number that I have seen posted here is 1-4% per day. Mine is about 1% in the summer and 2% in the winter

 

[exnisstech]

This is being over complicated for inaccurate results that are a guess at best.

Make a line in the sump with tape

Label date and time

Come back 24 hours and see if the water is lower. Take measuring cup and add water and see what’s needed to bring back to the line. That is your evap for 24 hours.

If not much loss noticeable in 1 day then wait 2 or 3 days and divide the water added by number of days

That would take all the fun out of it

 

[Pntbll687]

I think you are trying to complicate something that isn't that complicated.

Vintage Reefer has it above as to what you should do.

Mark the return chamber of the sump. Come back in 24hrs and see how much water it takes to fill back up to the line.

 

[Pntbll687]

That would take all the fun out of it

By fun, you mean trying to complicate something and sound way more important than it really is???

 

[exnisstech]

By fun, you mean trying to complicate something and sound way more important than it really is???

That's exactly what I mean. But to each his own

 

[Pistondog]

Certainly easier to measure than calculate.

 

[Pntbll687]

That's exactly what I mean. But to each his own

I forgot to add the sarcasm meter at the end bc of that!!

The sarcasm was dripping off my fingers as I typed it

 

[Ben's Pico Reefing]

What is the purpose of trying to calculate? Looking to find the right size container for auto top off in limited space for example, knowing how much to make to not waste? Or just curious as to what it is? As everyone stated, measuring gives you the best, but even then different times of year and weather will effect this as the home gets more humid or drier. How much your A/C works. Fans that may run longer or shorter if home or not and temp.

Best way is to make a graph and make a marker line. Record information when you top off or if an auto mark and note that as well. After one year you will have the average and a range. This can still even change year to year but shouldn't be to much. If you run humidifiers and dehumidifiers keep temp the same in the room (basically climate control the entire room). You can have accurate results in a couple weeks lol. But that's extreme lol . But an interesting idea.

 

[Randy Holmes-Farley]

As a very rough rule, most tanks evaporate 1-3% of the tank water volume daily. it will vary by season and location and equipment. Smaller tanks have a higher surface to volume ratio so will tend to evaporate more, all other things equal.

 

[MnFish1]

I was trying to calculate just generally what the evaporation rate is of my 42 gallon reef tank not considering it's 10 gallon sump which is in the cabinet. I use ChatGPT4 and put in the factors of room temperature 70°, humidity level 50% and water temperature of 81° and ChatGPT4 basically gave me nothing. I'm just wondering if I have 41 gallons of 81° water cubed tank how much generally should I expect evaporate in a day? one gallon.gallon . 1 litte? There's gotta be a ballpark figure at least . I understand. We also have to figure in the surface area of the water. Mine is a cube about 23 x 22". Any ideas just roughly about how much water I might be a evaporating in a 24 hour period? I know there's no way to come up with a concrete answer without doing a mathematical equation, particularly involving surface area of water and maybe surface temperature of water. what else is there? thank you.
edit, I think it's fair to say that if somebody has a reef tank that's 81°, and they live in a typical home with out significant humidity inside the house and you're in 70° room temperature that that water is gonna evaporate pretty quickly? Especially the differential between the warm water and the much cooler air. Not to mention the circulating water from the pumps and reef waves.

One way you can calculate it is carefully make a line in your sump at the meniscus of the water wait 2 days - measure the level again calculate the volume of the water by multiplying the inside length of the area measured by the inside length times the level of water decline. Do the measurements in cm. Multiply the 3 numbers together and you get the evaporation/water loss over 2 days. If you do it for 3 days or 4 days, you divide by 3 or 4. Note you need to use an area in the tank that will show a drop (some areas in the sump should remain constant. However, there can be a significant variation based on humidity, actual surface area exposed to air skimmer, etc which will make these calculations less valuable, and it may vary from day to day. Why do you want/need this information? I would not trust a measurement, for example to decide how much water to top off etc.

The amount of water loss should also be proportional to an increase in salinity over time IF you have an extremely accurate salinity meter. Again - the problem with nearly any measurement is going to be there could be pure salt water lost (splashing, skimmate, etc) as well as evaporation - so there is not a clear way to differentiate some of the variables.

The above methods should provide an estimate. Hope this helps.

 

[MnFish1]

so many variables it would be very complicated to calculate and then that would just be at one point.

measuring actual would be the easiest way

The number that I have seen posted here is 1-4% per day. Mine is about 1% in the summer and 2% in the winter

And as others have said - if it's 1-4 percent/day - that is a 4 fold increase or decrease (potentially). The other way to do it is to measure in 24 hours the amount of water that is added from an ATO system. However, very few of these measure purely evaporation, but also salt water that is lost through various means. And it also doesn't take into account any dosing which is added or water from feeding, etc. Which again brings up the question as to the reason for measuring it. IMHO the reason will dictate which method makes the most sense?

 

[MnFish1]

edit, I think it's fair to say that if somebody has a reef tank that's 81°, and they live in a typical home with out significant humidity inside the house and you're in 70° room temperature that that water is gonna evaporate pretty quickly? Especially the differential between the warm water and the much cooler air. Not to mention the circulating water from the pumps and reef waves.

It depends on multiple factors - some will increase evaporation, some will decrease it. It also depends on your definition of 'pretty quickly'. Clearly, water evaporates (which would be 'pure' water), but whole salt water is also lost in many tanks via splashing, skimming, etc. I don't know why you're wanting to ignore your 10 gallon sump (which is 20 percent of your water) - it should also be included.

 

[Ballyhoo]

i

so many variables it would be very complicated to calculate and then that would just be at one point.

measuring actual would be the easiest way

The number that I have seen posted here is 1-4% per day. Mine is about 1% in the summer and 2% in the winter

i thought more water evaporates in summer

 

[Treefer32]

As a very rough rule, most tanks evaporate 1-3% of the tank water volume daily. it will vary by reason and location and equipment. Smaller tanks have a higher surface to volume ratio so will tend to evaporate more, all other things equal.

I have a tough time thinking of evaporation as some factor of volume. For my 340 gallon display and 75 gallon sump (half full) I would be looking at an evaporation rate of between: 3.3 - 9.9 gallons per day.

In contrast my 125 gallon display I had before would have evaporated: 1.25 and 3.75 gallons per day.

I have a fresh water bin that auto fills with RODI once every 6 weeks or so, fills to around the 75 gallon mark.

6 weeks equals 42 days = 1.79 gallons per day that's using the same water to fill my dosing containers ( 1 gallon each and my 5 gallon of Kalk wasser that I'm dripping 24/7 into the sump). That doesn't take into account how much is removed by the skimmer monthly. I would say in a 6-8 week period, I'm looking at 5 gallon bucket full of skimmate. Factoring all the mechanical removal of water. I'm probably evaporating around 1-1.5 gallons per day. When I should have at least 3 gallons per day.

This is super critical because I was debating adding a kalkstirrer and realized I probably can't dose more than a gallon a day or I risk adding more than is needed per day for evaporation.

I even run a dehumifier in my furnace room where the display and sump are located. It keeps the room around 50% humidity. (It's the lowest I can go without it running 24/7).

I feel like my 125 (in a different home) evaporated way more than my 340 does. It was easily 2-3 gallons per day vs. what I have now.

 

[Timfish]

FWIW, depending on the weather I've from almost none to as much as 15% weekly.