K so been having this problem awhile now and starting to think it might be the dry filter food I'm feeding. It's New life spectrum filter feeder food but it expires in November it says.

This happened after I was at a drift show yesterday. WORRIED!!!!! It has happened before and been a week it's been happening. Sponge is starting to get grey in colour so in thinking its toast now but not 100% and the issue needs resolving! Using tap water but started this weekend on using RO by doing a water change and now too off water too.