Pale and unresponsive

I got two axolotls from a breeder about a month ago, and they have been living happily in a large tank together for a while. However, my tank has had a rather large build-up of brown algae recently, which I haven't have had time to clean off until today. The filter is not strong, and I've seen both of them playing with the water flow several times.

However, recently Cotopaxi (a wild-type) has been looking pale and hiding. I didn't think much of it, since he likes to hide under rocks a lot anyway. Today when I took him out I noticed him floating near the side, and managed to scope him out very easily, until every other time I've tried to get him out. He is very pale, and just floats in the water unless touched, when he wriggles a little then goes back to floating. Please can someone give me some advice on how to help him - I have no idea what's wrong and it's very scary. The other axolotl - Draco - has been swimming around normally and seems fine.

Never mind ><. After cleaning the tank I put them both back in and he's swimming around normally now. I feel really stupid for panicking, but he's apparently fine now.

hi
they do like to scare us......
lea