What happened to my Flowerhorn?

It may have been the Tubifex worms, although you can never rule out stress and shock from moving, but that is not typical for Flowerhorns.. However, in your case the new tank was large enough, pH doesn't matter much to Flowerhorns, and you say the water chemistry was normal. . They live in dirty environments and all Flowerhorn Websites say not to feed tubifex worms. Acaras don't suffer some of digestive problems that Flowerhorns are prone to, and can usually get away with eating them. There is no way any sane Acara will attack a Flowerhorn. Was the flowerhorn very active when you bought him. They should be really hyper in stores unless they are sick..

Flowerhorns are the fish most prone to Hexamita, a parasite which affects about 25% of them and they get it all the way back in Asia on the breeding farms. It takes many months to kill them, but it will if not treated with metronidazole (Seachem fishzole). They shock of aqwater change may have thrown the Hexamita into activity, but that is unlikely, and even freeze-dried tubifex worms can carry Hexamita and Spironucleus parasites according to Fish Geeks.. I also have seen stupid Flowerhorms get things stuck in their throats. One of miner ate a rubber band that fell in his tank and he gagged for a week untill I scared him into coughing it up. They do try to re-eat things they counldn't get down the first time. It is possible the freeze dried worms got stuck in it's throat. Unfortunately, without an autopsy, these are all best guesses.

What exactly were your readings rather than just posting fine .

The tank was not particularity big but often Adult fish that get moved from one home to another do stress and Die .