Danios isn't active anymore

Feb 12, 2018
Hi y'all! So when I decided to get an aquarium for my son (he's 2, really it was for us) I thought, this isn't too hard, I've had fish before, it'll be a piece of cake. Wrong. We've only had the tank sent up for about a month and a half and have 2 Danios an 2 tetras (all glofish). At first the danios were very active and the tetras reserved. I just assumed that was their personalities. Well now one of the danios has been very inactive hanging out in 2 areas of the tank, the top near the bubbles, and more recently the bottom. I haven't had the water tested since getting the fish but plan on doing so tomorrow. 3 days ago I found a dead roach in the tank (the joys of living in a log cabin) and almost immediately a nasty brown film started growing in the tank, mainly on the fake coral. Last night it had gotten so bad that I did a partial change and washed off the coral in hot water before i went to bed for fear of waking up to dead fish. I added water conditioner, stress zyme and stress coat. The heater is set in the mid to upper 70's(it's hard to see exactly where it is but the water feels like its room temp). Ive had different people tell me differently regarding care. What should I be adding to the aquarium regularly. How much should I feed them? I've been giving a small amount once a day but they always seem so hungry. What do I need to do to try to correct whatever problem has my one danios and 2 tetras stationary? Sorry for all the questions!! Oh and it's a 10 gal tank.