So I am pretty sure my neons have neon tetra disease. Out of original 16 there are now half this amount left. Been in the tank about 8 months now. How quickly would this disease spread and kill the neons is it fast? The remaining neons all look healthy apart from hiding at the back of the tank. Other fish are rainbows, gouramis, platies, corys and rams and all look fine and swimming around normally. So what next? I sort of feel like I am waiting for another tetra to die. I will up the water changes to twice weekly. One last thought....could liquid plant fertiliser be causing these problems?