Illness/Sickness: Axolotl Can't/Won't Put Down Hind Legs

[WooperZet]

This is my first post here, I've just been lurking around for info on here for the past few months.
I'm a relatively new Axolotl owner (had one for ~8 months), and I can't find clear information on my problem online, so I've decided to ask everyone here.

My Axolotl who is about 20 months old (got him when he was about one year old, according to the past owner) started to not put down his hind legs about a week ago. At first, I thought it was just a one-time thing, but he hasn't put them down for the whole week. I tried pushing them down yesterday (maybe a mistake), but they instantly returned to hanging at his sides.

For a description, he stands on his front legs, but sort of just leaves his hind legs hanging out to the sides. Sometimes he sort of puts down his right hind leg, but it never stays down.

A few sites said this could be a sign of sickness, but again, they weren't very clear. I can take a few pictures if needed. Any information would be useful.

Thanks!

 

[Wysper]

Pictures would be most helpful.

If you are concerned about a sickness, please post your water parameters as well. Temp and test results, etc.

 

[WooperZet]

Pictures would be most helpful.

If you are concerned about a sickness, please post your water parameters as well. Temp and test results, etc.

Water temperature is 19 degrees celsius.

Ammonia 0
Nitrite 0
Nitrate 51
pH 7.1
Here are a few pictures, they aren't too great - he's in a bad photo-taking position at the moment. I'll try to get some better ones when he moves. Both of them are pretty bad because it looks like his feet are just facing to the right/left, but they're really just floating there and pointing to the right/left.

 

[WooperZet]

A slightly better image of the left hind leg:

 

[Skudo09]

This is usually a sign that he may need to do a poo and is perhaps a little constipated. What are you feeding him?

The level of nitrate is a little higher than the recommended maximum level. It would be worth doing a water change to bring this down a little. It is recommended to keep nitrate below 40ppm.

 

[WooperZet]

My father who feeds him once in the morning while I'm at school says he pooped two days ago. I have yet to verify if he actually knows what his poop looks like...
We feed him thawed frozen shrimp and sometimes freeze-dried bloodworms.
I will try to do some more water changes.

 

[Cloppy]

I think it is definetly a gas bubble problem. Your axolotl might have hit a decoration or the side of his tank really hard and cause that bubble to shift. It is kind of like swim bladders in fish.