the last two betta's we put in my daughters 5 gallon tank died, ugh, All the parameters checked out fine. so I sterilized the filter and changed out 100% of the water and also treated with antibiotics, then let it sit for the last 4 days with the antibiotics. Today I did another 100% water change, I have sand and live plants in the tank so I don't really want to tear the whole thing down and sterilize the tank and buy new sand and throw out the plants, sooo... anyway now that there is fresh water in the tank I am going to let it sit empty for two weeks with just the plants and dosing fertilizer. in a week I was going to add one of the seeded sponges to the filter and then feed it with a drop of ammonia every day until we find a good betta for the tank. Once I find the betta he will be kept in a QT container with a heater and a filter for two weeks before going into this tank. So basically this tank is going to be 2-3 weeks without any fish in it, although there are still malaysian trumpet snails that have survived everything, and dosing ammonia will help feed beneficial bacteria and also create nitrates to feed the plants. I do dose seachem flourish as well but havn't since I treated and cleaned the tank.