I don’t test anything other than PH, Ammonia, Nitrites and Nitrates. If you think you’ve got OTS Id do small daily water changes (including gravel/sand vacuuming for a week until you’ve done 100%. I’d also rinse the sponges in your filters with tank water in a separate bucket/container. If you’ve got a lot of algea I’d scrub that too and maybe add some rock if you’ve got real low ph but i know bichirs like lower ph anyway (high 6 low 7). I think cleaning will bring everything up naturally. I’d say the key here is doing this slowly if you have fish living inside, if not just go crazy lol
I cycled my 125 with 6 bichirs and didn’t lose any, they are really hardy so I’d say you definitely have a problem if they aren’t doing well.
