Illness/Sickness: My axolotls keep dying, HELP

So I'm very new to all this, however I have done absolutely everything 'by the book' in accordance with the advice form where I got my axolotls. It's a bit of a story...

It all started about 3 months ago when I bought a pair of very young axolotls, at the same time buying a brand new tank/accessories/water treatments/food etc from the same store (an aquatics place). I was all set to go. Did everything I was advised to do in regards to caring for them etc, so I was pretty upset 3 weeks later when one (Hector) was floating at the top one day & then I found him dead the day after that. I brought the body back to the store & explained the symptoms. I also added that this one had no legs when it was sold to me so I was reckoning it was already at a disadvantage. They agreed & sent me home with a replacement. Meanwhile the remaining of the original pair (Tuco) was doing just fine. Until two weeks ago. Same thing was going on as with Hector but for a couple of days. I went back to the store for help and advice, spoke in depth with 3 senior members of staff for almost an hour, and by the end of it the only thing they could come up with was...nothing. Not a damn thing. They even tested the water and it was absolutely immaculate. I went home and spent hours online trying to figure it all out. The next day I bought something to treat swim bladder and also some aquarium salt. But it was too late, Tuco was dead when I got home from work.

Now I'm left with Hector's replacement, which will remain nameless for now because I don't want to get attached just yet.

I figured the water could possibly have been too warm so I bought an aquarium fan that I attached to the inside of the tank. This lowered the temperature a degree or two, nothing major I don't think. I've since replaced the entire tank with something I feel is more suitable. I have the fan going constantly which has the water temperature at a consistent level, Im feeding this one defrosted bloodworms every third day (as advised by the store), and I've taken pretty much everything out of the tank so that I can keep an eye on the Axolotl. Im also waiting on a delivery of new (clean) plants by courier tomorrow. I've started treating the water with the swim bladder stuff as advised by a local pet store employee & axolotl enthusiast (who gave me this advise when Tuco was on the way out but when I got home with the stuff it was too late). 'The last one standing' has been displaying similar, but far less dramatic, symptoms the past few days except it's the rear end is floating upwards a bit. It pooped today and it's less floaty looking. I know this can be a factor but I'm still not convinced.

At this stage I'm very disheartened & feel terrible about the whole thing & I'm absolutely babying this remaining axolotl. This is why I joined Caudata today, I feel someone here may be able to help.

First off, I'm so sorry that that happened to you! I know how hard it is to lose an axolotl, and it's something no one should have to go through. Anyways, I have no definite answer as to why this is happening, but it could have to do with the fact that you're getting your axolotls from a local pet store. Pet store's generally don't take care of axolotls very well, as you mentioned that you're first one had no legs. It's possible that the axolotls you adopted were not separated during their cannibalistic phase, causing them to attack each other. On a related note, the water condition they were raised in probably wasn't very good. It sounds like you were doing a good job with preparation and making sure your tank was ready, so it's more likely a problem with the seller rather than your care. I'd say the most logical explanation is as follows; the axolotls you bought most likely came from a diseased tank, and by the time you took them home, whatever sickness they had was too far to do anything about, thus they either attacked each other due to poor upbringing or died of sickness, but I'm not entirely sure. In the future, a better option would be to purchase axolotls from a breeder who cares a lot about what they do. Breeders that are reliable and in your area can be hard to come by, but it's worth it. Again, I'm so sorry about what happened, and I wish you the very best!