Water loss / evapouration.

[Dreadedlurgi]

G'day all,
I am just setting up a new fish only tank and I am surprised at the amount of water loss I am experiencing (no leaks). 1200 x 400 x 460 mm tank (4ft x 16 x 18 in). 300L (80 US Gals) including sump. Temp is 24-25 Deg C (75.2- 77 Deg F). Cover glass present on tank and sump. No livestock yet. I seem to be loosing up to 5 litres in as many days. Is this the going rate for evapouration? We are in drought conditions in Australia, and every drop counts down under!
Thanks, in anticipation of any comments.

[Poseidon]

Hi!

As for the evap rate, it is what it is. I lose about 3 gallons a day here, depending on the weather. In the winter it is worse then in the summer, as where I live it is very humid in the summer time.

Usually it is recommended to NOT run the glass covers, as this is better for gas exchange, and evaporation replacement water is often saturated with lime before being placed back into the tank to help with Ca and Alk levels. In your case, I think the glass covers are the best choice.

To help solve your evaporation problem, can you enclose the room your tank is in? If the hot dry air from outside is not allowed contact with your tank, the evap rate will drop. I know this may not be practical, but it is the only option that I can think of.

[weez1959]

My evaporation rate is about 1 gallon a day depending on humidity. An auto top off is really indispensable on my tank
As for closing off the room, I have horrible pH fluctuations if I do. If I leave the window to my sump room closed the next day my pH is at 7.8-7.9, then if I open it up again it goes back up to 8.3-8.4, so for me closing it off is not an option even in the winter.
I also wouldn't use glass covers, not a good idea...

[Dreadedlurgi]

Thankyou ver much for the replies. By the way, why are glass covers such a bad idea?

[weez1959]

I guess in my case the glass was bad because I was having to constantly clean them to let the light through and with a closed tank my pH was horrible.

[Ninong]

Glass covers are a bad idea because they limit air exchange and because they increase the water temperature by trapping heat and restricting evaporation, which is cooling.

I have no experience whatsoever with evaporation in a tank with glass covers, but in a normal setup, you can expect evaporation between 1 - 2% of the total water volume daily depending on your lights and the ambient humidity in the room.