The problem was mainly due to me feeding 12-18 market shrimps every other day with 10 massivore pellets, 30-40 hikari stixs, and 3-5 frozen feeders. This is all in one feeding. I cut back on market shrimp feedings from four times to two times a week and the water stay crystal clear for the whole week without any sick bichir. I would test my water to do the experiment but my water never had ammonia or nitrate. I am guessing that the ammonia level is so low that the API test kit didn't pick up. If you're having filtration or water problem issue then I hope this tip would help you out.
In addition, I also sold 5 bichirs.

In less than one week I picked up 5 new bichirs!
In addition, I also sold 5 bichirs.

In less than one week I picked up 5 new bichirs!
Maybe you guys shouldn't have so many polys in the first place? Who am I kidding that'll never happen