Floating axolotls

Guys, my 3 axolotls float and have done for many months. I've tried everything to help them but nothing works. Caring for them is no fun any more and has turned into a chore. Feeding is damn near impossible and the tank is so depressing.
Does anyone know how to fix them?
If not, what is the most humane way to euthanize axolotls?

Woah, woah, woah... Don't be so quick to bring up the possibility of euthanasia. Axolotls are really resilient animals and can come back from a multitude of hardships. Could you be a little more specific about what's going on? Do they try to swim down but cant? Are they still eating? Do you see any poops in the tank? It's possible that they have an obstruction that's causing them to become constipated, which can cause uncontrollable floating in axolotls. What does your substrate look like?

Thank you for the reply. I was beginning to think I would get none.
Euthanasia hasn't been quick. I've been contemplating it for almost 9 months.
They try to swim down but they're just too buoyant. It seems to stress them to no end. I've given them hiding spots at the surface which they do enjoy.
They do still eat with one difficulty. Poops appear sometimes but it's usually a weekly or fortnightly explosion. Is this usual?
My substrate is really fine white sand. There's no way that could be blocking anything i think.

I've decided two more strategies to do before I consider moving them on.
1. Feed feed feed. I'm going to put in much more food to try and force whatever is in them hurting them out and get their digestive cogs turning again.
2. Change of scene. Just to be sure that it's the Axies themselves to blame not my setup, I will shift them to a whole new, clean, empty tank to see what goes on.

Oh yeah of course! I saw this thread and I was hoping another person with a lot of axie experience would come along and help you out, instead of lil 'ol me lol.

Are they bloated at all? And when they do poop, do they stop floating? Also, what do you feed them? Some diets tend to plug up axies more quickly than others. I still feel like this has something to do with an intestinal blockage of some sort. Have you tried fridging them at all? That is typically a method used to let whatever is blocking them up pass, and I know there's a good sticky on it in this forum.

No, they don't seem bloated to me. They seem rather proportionate as far as axolotls go to be honest.
When they poop it doesn't effect their floating no. At the moment they feed on pellets designed for axolotls. Having said this, they started floating while I was feeding them live home farmed earthworms and I switched them to pellets after they began rejecting the worms. They eat the pellets with relish and won't take worms anymore. They just throw them up or ignore them.

I did try fridging a couple times, put them in a little container with water up to their backs, wrapped them in a towel and put them in the fridge for about a week. They stopped floating at the end for about 4-6 hours then they went back up and behaved as usual. The tanks temperature never goes above 20 degrees and is commonly about 18 degrees.

Hmm... That's so strange. Do you think the pellets are making them gassy? Have you tried feeding them anything else? Honestly if they're still eating I wouldn't euthanize them. This may just be one of those issues that works themselves out with a change in diet, time, etc... Though I understand how frustrating and depressing it can be.

I've changed the type and brand of pellets I feed thrice now, nothing changes. It's all very strange I agree. And so you see my predicament. I'm truly at a loss from here. If the extra feeding doesn't work in a couple weeks I'll try separating them off into a new environment for a little while. Then if they change I'll clear out the tank as it is and leave it entirely bare for them. If they don't change then, I don't know what to do.