Be care with the towel over the tank, keep an eye on the tank, if possible. I put a couple of towels over my 10 gallon tank for 3 days to treat Cyanobacteria, it worked but the towel also pulled over 1/2 the water in my tank out of there. The towel wasn't even hitting any of the water, it just absored it and the smell was horrible! I would recommend using a sheet or some heavy plastic in the future.