i know you can make it by putting a flat stone in some water in a plastic bottle but how much water does it have to be in and do you get water from the tank or tap water? how long does it have to be left in the sun?
I'd use tank water following a water change but I don't think it makes a lot of difference. Reason I say tank water is I know algae grows in that, and can't say I know about tap water.
Works with either, in a bowl, covered with enough water to completely submerge, leave in sun for a couple weeks Sun - ha if we ever get any again that is