Just reading up on other bichir posts because I have the same question about mine growing so slow, but an off topic suggestion the ammoina tester you have on the aquarium is not sensitive at all. I had one with read 0ppm ammonia when I get it tested at the pet store the very same day and its .4-.5ppm!!!! So I would reccomend the api liquid test kit that comes in 2 bottles.
and make sure your bichir can reach the top of your tank for air! (sorry if I'm telling you facts you already know)
and that is a beautiful tank, I love the plants floating at the top, I might have to steal that from you for my own ; )
good luck with the fishkeeping!