Illness/Sickness: Unsure of what's wrong-Please help!

Hello everyone! I came across your wonderful community while researching axolotls and am thankful this resource is here. I got 2 leucistic axolotls in late July from a somewhat local breeder. They are being kept without substrate and light at the advice of the breeder. It is a 29 gallon tank. I have 3 hides and ledges set up. I have a canister filter and a chiller that is set at 65. The first couple of weeks the flow was pretty heavy but I sonce lowered it upon reading the hard flow stresses them out. Since then I see a while slime on surfaces. When I do water changes I clean it off to the best of my ability. I'm using only Reverse osmosis water and no conditioner although I do have prime. The breeder suggested another brand, microbe lift so I have that. Everything was fine until last week one of the axolotls have stopped eating. I was feeding red wigglers and they would eat one a day sometimes two. Although sometimes when I fed 2 I'd find one regurgitated. I've also been using hikari carnivore tablets. I have fish tanks so I would also give them some of the thawed bloodworms and brine shrimp. My main concern is the axolotl not eating. He/she also appears a bit listless, which would make sense if not eating or feeling well. I have seen him attempt to eat but swim away. I dont know if it's wishful thinking but I think he may have eaten a like maybe one or two free floating bloodworms. I offered some directly to him as he was sitting close to the surface on a soapdish and we wasn't having it. The other one is fine. The water quality is fine for the most part. I will post as many pictures as I can. Thank you in advance for reading and any advice is welcome!

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The light is on for examination and picture puposes. This is the setup. The one in soapdish is the one that eats. The one on the blue pump is the one I'm worried about. I haven't used feeder fish or ghost shrimp for fear of disease or contamination. I use only one siphon for them and a waste bucket for them so contamination from a fishtank is unlikely. I try to change the tank every 3 to 5 days. (Once or twice a week) Usually 10 gallons at a time

Hi, firstly was the tank cycled prior to adding the lotls? What are all the parameters including GH (hardness)? Are you remineralising the water, as RO water isn't safe unless you are adding the minerals that they need.

If your tank is cycled I would try replacing the water slowly with dechlorinated tap water, or water that isn't RO water. RO water is stripped of everything, including dissolved salts or minerals that many animals do need.
I would reccomend finding a simple dechlorinator that also removes heavy metals and trying that out.
I wouldn't do the change all at once, don't want to shock the system or kill off any beneficial bacteria.
The axolotls could just be reacting to the RO water as you have a chiller and I'm assuming a cycled tank.
Keep trying to offer food, if you have access to night crawlers try those as they don't taste as bitter as red wigglers.

Thank you, yes, I actually had a great talk with the breeder and that was the missing key-the ro water! So I remineralized it today and moving forward I'm going to use tap water and the conditioner she uses and hope for the best. I will do a slower transition as not to shock them. When we had spoke she had said another owner uses ro water but didn't think to mention the remineralizing part. I keep planted freshwater aquariums and use it in those but ironically I didn't use it as I wasn't sure if it would irritate their gills or skin. I feel terrible and hope that the little guy will bounce back. I find it odd that only one has been suffering but I'm hoping to get na good quality of life back now.