Cherries dying off one by one
I have a small tiny group of cherries in a separate tank (5.5g) and I do about 20% water changes each week. My question is, why are they dying? I don't add ferts to the water and the levels for ammonia, nitrite and nitrate are all 0. I may also add that pH is around 7. There is planaria in the tank and I've been trying to get rid of these guys by trying to lower the amount of food I add to the tank/doing water changes? Does anyone know what's going on?