just one strange possibility, try rehoming your clown loaches for a week or 2, see if you have a massive trumpet snail issue.
I had a tank that was trouble, moved the loachs out of it and 1hour later the thing was litterally covered 2 deep with MTS, nuked tank and started again, no problems since, though with the loaches it had been going on for 6 months.never saw 1 MTS (Nitrates through the roof in 2 days due to massive bioload)