Question: Larvae Water Changes

Hello all! I have 3 young axies (front legs, no rear) that are on a BBS diet with blackworms as an additional feeder. I have all 3 separate in 1 gallon jars filled with about 1 1/2" of water. These 3 jars are then inside another, larger tupperware container filled with water, which is on an AC vent, so the water is pretty consistently at 15C. Before I put them there I was icing the water off and on and it would vary from 17-20, usually hanging out around 19C.
I keep them in jars submerged in other water to hopefully keep the temperature more consistent.
Anyhow, since they are in such small amounts of water, I am wondering if I should be doing more then partial daily changes. I change all the water every other or every third day. I know this is stressful--but I can't think of another way to keep the water cleaner. The daily partials are not enough. Should I put them in more water? Move them to the 20? They don't have rear legs yet & I don't want them to cannibalize each other so I am keeping them separate.
Can you help me figure out a better way?

I raised mine in shoe box sized tupperware containers. I would drain the water with air line tubing, using it to get any debris off the bottom. I drained almost all the water daily, leaving the water level just above the gills.

I have another container of dechlorinated water ready (I keep this container in the same area as the axie so the temps are the same), put it on a surface higher than the tub with the axolotl in it, then siphon the new water into the tub with the axie. The air line tubing is small, and the water is slowly trickling in reducing stress. I had about 3 inches of water in my containers.

I hope that wasn't confusing!