Well somehow my water evaporate fast. Like if i refil it to the top of my tank, it will evaport about 3 inches of water in only 3 days. Also that makes my specific gravity go up too. Is there anyways to fix this?

3 inches of water evaporating in just 3 days seems like alot. Are you running intense lighting, closed canopy, etc? You could purchase a Auto Top Off system although they are quite expensive. You could also build a DIY Auto Top Off which there are many plans out there especially on Nano-reef.com. If you don't want to use a ATO then you would need to keep up on topping off.

I'm not running on intense light. I might add a piece of glass to cover the top.

Check out www.aquariumconnection.com. They have an auto top off system that's pretty top notch for 150 dollars. It's an investment, but a worthwhile one if you are having problems keeping a stable sg. I know my tank evaporates water like crazy. I run an open top with two 96 watt lights. Of course, it's a 29 gallon, so even a little water seems like a lot.

Good luck and let us know how it works out.

I'll try looking into it.

I add about 1 to 1and 1/2 gals of water a day to my saltwater tank. I do have halide lighting though.

Ok.