Clownfish with a brown Mark help please

[dez_newman]

So my tank had cycled in 4 weeks (300 litres) and I had 3 green chromis in it for a week. All levels were fine. So I added a clean up crew of 8 snails a emerald crab I also moved my 2 clowns and a shrimp from my quarintine tank across as the ammonia had spiked in the qt tank. Below and behold my tank went into a full cycle. Ammonia 1 Nitrite 0.75 and Nitrate 10. The following day Tuesday I went and added two bottles of atm colony.
Wednesday the ammonia was back to .25 nitrite 0.25 and Nitrate still at 10.

So today the ammonia is at 0 nitrite is nearly 0 and Nitrate is 5. I have Just done a 50 litre water change but I did notice that one of the clowns has a lump on his chin his mouth seems to be open more than usual as if he is gasping a bit. please can some one tell me what it is. It is a Perc and seems to be swimming around ok and the two of them have been fighting a bit.
Don't want to loose the little guy.
Thanks
Dez

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[dez_newman]

Further to this I have got a major diatom bloom even with some on the surface of the water !!

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[dez_newman]

Also forgot to mention that I have also lost at least half the snails and I have haven't seen the small emerald crab in a couple of days. Yet the cleaner shrimp seems to be ok.

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[Phil077]

Are you sure There not just cleaning the rock dez?
I Have had percs with battle scars before. Having said that keep an eye on them
imo you might have added the cuc to fast.
Nout in there to eat.

 

[dez_newman]

Perc seems a little happier after the water change. Will just keep an eye on everything.

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[CEECH]

If using colony take tge cup off your skimmer for tge week. Will airate tge water more and help boost bacteria. Works a treat. The cuc would not have liked ammonia

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