Scared about my afericans

[crb530]

so after cleaning the salt tank i had to move to the aferican tank for a water change and cleaning

well when i looked into the tank every fish was acting weird then i look at the pictis cat and it is just covered in ich

every thing was alright yesterday

so right away i did a water test and my nitrates where a little high 40ppm but thats normal for my tank befor a water change

any ideas what could have happened

i realized the tank is getting to small but there is a new tank coming on friday

right now there are 5 cichlids sizes 3 to 5 inches and 1 ranbow shark 4 inches 1 picis cat 3 inches and the one red devil crab size of my palm there is no agrestion in the tank its a 37 tall with a 20 gallon sump and on friday they will be moved to a 60 gallon with 20 sump

any ideas what could have gone wrong