Illness/Sickness: I think my axolotl might be ill

Hi, hopefully somebody can help me.

My axolotl doesn't seem right. He has been swimming about lots and bumping into the glass which I know is a sign of a stressed axolotl Also, he lost the end of his tail in one of these mad swimming about the tank sessions and I'm not really sure how. Just him, some plants and his filter in his tank.

I've checked his water with 6 in 1 test strips (do this every week) and this is fine, his water temperature is fine and I don't think he is under/overweight because his tummy is about the same size as his head.

I noticed today (when I was feeding him, hence the bloodworms in one of the pictures) that his gills don't seem right. One side has gone very messy looking and the stalks the gills come off are very pale in colour. There also seemed to be some white bits on the gills? He hasn't eaten either, and this is the first time. He's normally very greedy.

Is he sick? If he is, how do I help him?

How big is your axolotl? The first thing I noticed is how tiny the blood worms look compared to him. If he is around 10cm you should try feeding him earthworms (night crawlers are liked better) or pellets. Another thing you could try adding could be a cave, it could be something as simple as a PVC pipe.

If you can, I would also invest in an API Freshwater Master Test Kit, as the test strips are notorious for being wrong. To minimize error, you have to follow the instructions very strictly, but the API test kit is much easier to use and read.

Could you give the actual numbers of the parameters? Ammonia, nitrite and nitrate at least, and also the temperature of the water. This will help figure out if there's anything wrong with his tank causing him the stress.

He's definitely bigger than 10cm. He sometimes has crickets but was told by a petshop this wasn't giving him all his nutrients so to feed bloodworms/brine shrimp too? I tried him on pellets but he wouldn't eat them, constantly spits them back out a few minutes after eating them. I've not tried earthworms, I'll have to try. I wouldn't want to get them from my garden though because my parents put all sorts of chemicals on it to make the flowers grow!

His temperature is 19 degrees
chlorine showing as 0
nitrate i between 10 and 25, closer to 10
nitrite 0
PH 7.6
carbonate 6
general hardness 8d

These are all within the ok reading on the packet.