Welcome to Fishlore.
Sorry to hear about your losses so far.
Excellent advice above.
A few more things:
Brown spots are likely diatoms, a type of algae that seems to thrive at the tail end of the cycle. It usually goes away on its own after a few weeks, though excessive light/nitrogen can give it a chance to stay. (I have a
goldfish/koi tank that gets lot of indirect sunlight that has a near-continuous diatom problem)
Yellow stuff is likely just nitrogen and algae staining the rocks. Not necessarily a bad thing, though it can be an indicator of poor water quality.
As Lucy said, daily water changes are going to help keep your fish alive (the GloFish will survive nearly anything, anyway, but no reason to stress them more than necessary). Once you get down to 0 ammonia and nitrites, your tank will have completed the cycle. After that point, do water changes to keep the nitrates below 20, and you're good to go.