Shrinking gills

In my big tank - it’s a 50 gallon with 4 adult females - I have a 120 gallon canister filter, as well as a 40 gallon in-the-tank filter. I change about 1/3 of the water every week, and I replace the carbon in the filters once a month. I use Prime. There are live plants to help with water conditions and reduce water flow.

My girls all seem to have gill issues. My copper had beautiful, long, feathery gills, but now has little gill stubs left, without much feathering at all! The others have more full gills, but sill less than they used to have. This seems to have happened over the course of a few weeks in spring. I thought it might have been because the temps got too hot for them. So, I invested in a window air conditioner for that room. But, while they don’t seem to be still shrinking, they also aren’t really growing back.

Someone on this forum suggested that the water is highly oxygenated, so their gills shrink because they aren't using them as much. It was recommended I remove one of the filters.
Does this sound right? Sounds very plausible to me, but I wanted to run it by the group.
Any ideas?

That is what I have heard too. The more filaments on the gills means there is less oxygen in the tank. However, I don't think having short gills is harmful. If you would rather them have long luscious looking gills though you could try to turn off one filter.

In my experience, I actually found when the water quality deteriorated, my axolotls would lose their gill frills. Once I clean the tank, the filter, and do a good water change, the frills would come back within a week. Turning off one of your filters may do more harm than good.