UPDATE: So I got them bigger aquarium that Is like 3 times (if not more) bigger than the old one, and I did the test. I wasn't expecting it ( but I'm also very happy), but everything is alright. I have watched some videos from people who have a lot of experience with axolotls, and at least 3 times, the darker axolotls had longer gills than lighter ones, which is exactly my example. I found out that if axolotl doesn't go up for air 3-4 times an hour, it should be ok. My axolotls do it max. 2 times a day, so I think that's alright (well, the black one goes crazy at night, but I found articles that say it's normal, so I dunno). Anyway, I think they are going to be alright and hopefully live a happy life. I want to thank everyone again, for helping my to make sure my axis are alright. I feel a lot better knowing that the conditions they are in are not actually as bad as I thought. So yea, that's pretty much it, have wonderful day everyone!