So I have been running a custom sump for about a year in my 75 gal
cichlid tank, it was made from a 29gal aquarium and worked like a deam. A few pieces on it were coming loose and I had the chance to get another 29 gal
for free. Long story short I used silicone that was kitchen use approved and 100% silicone, but SURPRISE, it had a mold inhibitor in it anyways. After about a day I noticed my fish were very lethargic, their color was faded and a few were dead. I did two 60-75% water changes hoping whatever it was would come out of the water but after a day several more had died so I went out and picked up a fluval 406 canister filter, filled 4 of the 8 compartments with carbon, and performed 2 more 50% water changes last night. The remaining fish seem to be doing better this morning but still obviously sick. Anything else I should do or just keep with a couple water changes a day for a few more days and hope for the best?