How fast do open-top tanks lose water?

shrimpyay

Weird question, but I've got a tank I'm cycling that is open-topped. It's got a built-in homemade filter setup and I'm having some trouble maintaining the water level in the last 2 baffle chambers of the filter area. All I can figure is that maybe I'm losing water due to evaporation faster than expected.

So, to those who have open-top tanks, how often do you see water levels dropping (to the point you need to add more, whether at a water change or between)?
 

StarGirl

I had mine open over the summer to not hold heat. They did evaporate faster than with a lid. I just added water when it started making too much noise or waited till I did my weekly water change.
 
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Cody

Weird question, but I've got a tank I'm cycling that is open-topped. It's got a built-in homemade filter setup and I'm having some trouble maintaining the water level in the last 2 baffle chambers of the filter area. All I can figure is that maybe I'm losing water due to evaporation faster than expected.

So, to those who have open-top tanks, how often do you see water levels dropping (to the point you need to add more, whether at a water change or between)?

Its faster than you would expect. Some depends on your home and climate as well. In Wisconsin it gets very dry in the winter months which leads to pretty fast evaporation. There is a good chance you will need mid week top offs if you want to go open top. I have open tips on my breeding setups so I don’t mind since I do two small water changes regardless so it’s easier to compensate.
 
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MrBryan723

My 2 gallon loses about 8oz a day. My 100g loses about 8 gallons a week. Both are around 80 with the average humidity outside being close to 50%.
29 g loses about 3 gallons a month. It has a lid.
 
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UnknownUser

It was a lot faster than i expected in the 90° heat this summer. I had a lid with half the top open all day and closed at night and I had to top off every 2-3 days.
 
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HolyKamikaziBetta

Weird question, but I've got a tank I'm cycling that is open-topped. It's got a built-in homemade filter setup and I'm having some trouble maintaining the water level in the last 2 baffle chambers of the filter area. All I can figure is that maybe I'm losing water due to evaporation faster than expected.

So, to those who have open-top tanks, how often do you see water levels dropping (to the point you need to add more, whether at a water change or between)?
I have to add water to my 60 like every day. It loses water fast
 
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RayClem

There are a lot of variables affecting evaporation:

The area of the tank- (a 20 gallon long will lose more water than a 20 gallon high a
The temperature of the water- the higher the temperature, the more rapid the evaporation
The humidity level of the room- if you live in a humid environment, less water will evaporate than if you live in a dry climate.
The degree of agitation to the water surface- the greater the agitation, the greater the evaporation

With the relative humidity around 50%, I might lose about 1 gallon of water evaporated daily from a 55 gallon tank and proportionately less from smaller tanks. However, in winter, when the relative humidity drops, I will have to replace significantly more than that.

Remember that when water evaporates from your tank you will only lose water, not the minerals in the water. Ideally, that water should be replaced with water purified by reverse osmosis or distillation. If your tap water is soft, adding tap water to your tank to replace evaporation is OK. If your tap water is hard and you use it to replace evaporation, the concentration of minerals in your aquarium will be ever increasing. Eventually, you will need a massive water change to keep the mineral content from getting too high.
 
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shrimpyay

Thanks for the replies everyone!! I had no idea just how fast it would be happening--some of those rates blew me away!

It's a relief to hear it's just evaporation causing my issue (probably) and not just me having designed a terrible filter system, lol. It makes sense--the humidity has been dropping fast as we go into fall/winter, and I've been noticing it making my skin dry...would make sense it's affecting the evaporation rate. Doesn't help that this tank has a waterfall acting as the filter, so there's both a lot of agitation and a lot of exposed surface area. For now I think I'll keep a really close eye on it and have a gallon of dechlorinated water sitting around so I can put a cup or two in every couple days as needed.

RayClem
Great points! I was aware of the evaporation/minerals issue, but it's always good to restate it just in case. Our water is pretty ridiculously soft out of the tap, so most of my attention is on adding enough minerals in to keep the snails, shrimp, and fish happy. Weekly water changes will probably also help, not just topping off. In our case I don't expect it to be too huge of a problem, but I will keep an eye on KH and GH, and might look into getting a TDS meter.
 
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DuaneV

Depends 100% on the climate, but my 20 gallon Im sitting next to loses about a gallon a day on average. When its really hot in the middle of the summer or really dry in the middle of the winter, a little more than that.
 
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Pfrozen

I have an open top 20 high and by the time it drops enough to top off its water change day anyways so it hasn't been an issue for me
 
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John58ford

There are evaporation rate maps available to break it into yearly amounts in a body of water as measured by inches of depth lost. These assume the average wind, heat, humidity etc. That you would have outside. Some people's homes are significantly less humid inside than out due to air conditioners, others are more humid than others due to swamp coolers. Others yet, are basically outside, but with walls.

In my area, it is said that a body of water over a year will lose about 20" of water. But there are places in the south that average 80+ inches lost. Pretty expensive to keep a pool down there I bet.

The map I have up currently shows Tennessee to lose ~40 inches per year outside. Add climate control with humidity adjustment to your house and now that means nothing lol. None the less, I find my glass lid covered tanks to lose about 1/8-1/4" a week, my plastic hood tanks 1/4-1/2" per week, and the mesh top tank has me putting in about 1/8" of water per day. I do not use anything that would control humidity in my house, and that rate of evap is more than twice my states rated amount, likely due to the constant flow and high relative temperature of the water.
 
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smee82

I lose water to evap more then twice as fast in winter compared to summer and need top offs every 5/6 days.
 
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JamesJunior97

Weird question, but I've got a tank I'm cycling that is open-topped. It's got a built-in homemade filter setup and I'm having some trouble maintaining the water level in the last 2 baffle chambers of the filter area. All I can figure is that maybe I'm losing water due to evaporation faster than expected.

So, to those who have open-top tanks, how often do you see water levels dropping (to the point you need to add more, whether at a water change or between)?
Weird question, but I've got a tank I'm cycling that is open-topped. It's got a built-in homemade filter setup and I'm having some trouble maintaining the water level in the last 2 baffle chambers of the filter area. All I can figure is that maybe I'm losing water due to evaporation faster than expected.

So, to those who have open-top tanks, how often do you see water levels dropping (to the point you need to add more, whether at a water change or between)?
Hi Shrimp, as far as my knowledge goes, there are only 4 factors that affect the rate of evaporation, that is temperature, surface area, humidity and wind speed.

Temperature because the warmer the water is, the more energy the particles have to move around (heat energy -> kinetic energy) and breakthrough their state of matter. For example, boiling water in a kettle evaporates faster than water at room temperature in a bucket.

Another factor is surface area.The wider the surface area the more space water can "escape". For example, water evaporates from an open bucket quicker than water in an open water bottle.

Thirdly, humidity. If your surrounding is very humid, evaporation won't be very fast. Although the temperature of the air plays a part in this. Warmer air has a higher vapor "capacity" than cold air. Once the surrounding air closes in on its vapor capacity, the rate of evaporation will slow down till it reaches zero. But that's only when the air reaches its "limit".

Lastly, wind speed. I won't get too much into this since this will be a controlled variable in your case but for consistency's sake, laundry dries quicker on windy days than any other day.

So back to your question, in my case water doesn't evaporate fast but then again I do 2 water changes daily (waste removal sessions) so I won't notice. However, in your case, you need to keep in mind on the location of your tank (indoor or out), temperature (if the day is warm) and surface area (wideness of your tank-top)and make your judgement accordingly. Add new dechlorinated water when you feel the water level is too low.

Another very important note, keep in mind when water is evaporating, the other elements and contents in the water do not. Concern should be taken on Ammonia as it does not evaporate along with the tank water and only makes it more concentrated hence poisoning your tank inhabitants.

I hope this answers whatever it is you are seeking.
 
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