My tank is just a mess. The same day the water started to clear showing signs of cycling the levels lowered I made a mistake and left fish food out. My 4 yr old took hole bottle and dumped in tank. Stayed up til 2 am removed all gravel washing and rinsing and washing in hot water. Did 30 % water change too. Water has not been same since. Took water to local fish store they said water ok. And I could add fish. But I did and they died. Soooo mad I went and got some clear away and after 2 doeses NOTHING CHANGED. . So I upgraded last night to new filter system. .. was thinking of just using same cartridge as it would fit new system but bobby said no. Use brand new ones. So thats were I am at. I have 1 neon tetra left with 4 platies. Soooo tell me what to do.... remove gravel and most of water and start all over??? I DONT WANT ANYMORE OF MY FISHIES TO DIE!