Frankly, I don't trust the test strips much abut we'll deal with them since that is what you've got. Disregard the hardness (GH) test, it has no value in this situation.
Since both tanks are showing nitrites, they are trying to start up again.
Am I missing an ammonia reading?
It boils down to this, if there is an ammonia or nitrite reading the tanks are either recovering from pH crashes and/or they cannot sustain the amount of ammonia present in the tanks. It's critical to maintain the KH level over 100, 120 is better as in start up. The filters (bio bacteria) are consuming the ammonia and nitrites (acids) in greater amounts.
Nothing in the behavior you are speaking of is outside of what is very common with pH crashed water. That is why we are stressing the need to stabilize the water, ASAP. Stable means zero ammonia, zero nitrites and a KH value above 100, 120 is better.
So many of the things that can present as parasites are also the things fish do when the water is out of whack.
Rule out water as a cause then deal with what you see once the water is stable. Fish have only so many ways they can indicate to us they aren't feeling well and their responses to water quality are not dissimilar to illness or parasites.