Lots of axie questions

We recently purchased 2 axolotls for our son for Christmas as he is fascinated by them. We have a 3ft tank, with internal filter. We have diffused the water flow by angling the water jet onto the wall of the tank. We also have a bubbler fitted and there doesn't appear to be a huge current of water.
We are on tank water - so no chlorine - but the aquarium gave us water conditioner and something called stress coat (dechlorinator and conditioner - has aloe vera in it for the slime coating) to use when filling/changing water. We had sand at the bottom (but it is quite coarse) but that is now (after reading this site) covered with much larger pebbles. We have large rocks, driftwood and plants for places to hide. We have been doing regular water changes.

We bought 2 axies - one slightly larger than the other. The aquarium told us they were both female. The bigger one seems to be doing really well - good appetite, big fluffy gills.
The little one seems to be struggling. She has much shorter gills and not much fluff on them. She has been bleeding from her gills too, and I was worried about a fungal infection as I saw some white fluffy stuff round her gills. My partner said he saw the other axie snap at her gills. I haven't seen her eat - but can't tell for sure as she may have snapped something up overnight/when not looking. We are feeding earthworms.
She seems to be going to the surface a lot to get air. I also saw her poo tonight and it was quite a bright green - and her cloaca seems to be enlarged compared to the other axie. I'm worried that she could have swallowed some of the coarse sand?

So - we have done a salt bath and put her in the fridge (it's at about 8 degrees). We've got another bowl of water waiting for her water change tomorrow. What else should we do?

Oh - and when you put them in and do water changes, do you pick them up and move them, or scoop them up with something?

And when we want to take her out of the fridge - do we just gently allow the small container to come up to room temp and then transfer back into the tank?

Sorry for all the questions. Of course, the smaller one is my son's favourite, so we want to make her all better! Thanks so much.

Hi
1 make sure the other bowl of water is at the same temp gently pick axie with a damp clean cloth and place it in new water.

2 When ready to take out cover bowl and leave to get to room temp have a look at axolotl.org

Using a cloth will be much more stressful than just scooping them up with wet hands. You run a major risk of causing abrasions.

Why did you put the axolotl in the fridge?

She was bleeding from the gills and one of them looks damaged. Also she seemed to be gulping air a lot. Generally doesn't look too well and wanted to give her a chance to rest up.

Is this wrong?

Anyone else got any ideas?

if the gills look damaged then that could be a cause for her to gulp air.

i'm surprised noone has said it yet but it you have 2 axies then its possible that her gills have been nipped by the other 1. If this is the case then she will soon regenerate any gills that are missing.

If one of the axies is a lot smaller then the other, the big one might bully the smaller one, and that can cause injury.
To test if this is the case, you can put a separator in the aquarium to keep them from touching eachother. If this seems to work, keep it that way until they are about the same size and them try to remove the separator to see if it all works out.