Beginner Gardening: Maidenhair fern plants dying!!! Please help!!, 1 by pruant

pruant wrote:
My two indoor maidenhair fern plants have been consistently dying since I bought them in July. In both pots, the few branches that still remain look dry and black (no longer healthy brown like before), there has been no new growth in the past month or so, and all the remaining leaves curl up and scorch out - even the few, really rare ones that manage to grow. I water my plants with warm tap water (hard water, I think) every other day, and pour water in the pebble tray once or twice a week to raise humidity around the plants. I fed it with Miracle Grow slow-release plant food once, but then the leaves started to scorch out. I later read that the dosage was too strong, and that too much fertilizer is not good for these gentle things. They get very filtered sunlight through the curtains.

To add to things, I've been noticing a whitish-yellowish crystalline coating on the outside of one of the pots. I've tried scrubbing it off a few times, but that stuff keeping coming back in just a few days. I used to think it's the minerals from the water or the plant food leeching out of the terracotta pot, but I'm not so sure anymore.Then there's also white bugs floating in the tray water, and some on the top of the soil. They are so tiny, I hadn't even noticed them before. Even now I can't tell the structure of these bugs (will attach pics). I clean out the water every two weeks though. I'm really sad looking at my plants. Where am I going wrong? Is there anything I can do to make them healthy again? Thank you in advance.