I am cycling my tank and i have a few losses, 3 were already ill from the shop Now i have 3 fish (2platys, 1 guppy) for cycling my 20 gallon. The nitrite levels are high from when there was a larger number of fish and i'm worried that i haven;t got enough fish for cycling. When the tank does cycle and i add more fish it will go through it again. Do you think i should add a couple more cheap, hardy fish such as cherry barbs to help the cycling?