i'bought an algae treatment that contains copper sulphate but i'heard it may be poisonous to axalotls any advice before i use it?
I wouldn't use copper compounds with axolotls.
If you're trying to get rid of algae I wouldn't use any kind of petstore remedy. Most are gimicks and don't work well or at all. The easiest and most efficient way to get rid of algae is to try to figure out what is causing it.
Algae begins to grow when the tank has too much potential food in it. Potential food can be uneaten axolotl food that is rotting in the tank, dying or dead plants, too much light, any sunlight that hits the tank or not doing enough water changes.
All of these things can lead to the buildup of nitrogen compounds in the water that are basically algae fertilizers. Look at your husbandry methods and try to change the things that are causing algae growth. Keep your aquarium light off unless you are watching your axolotl. Move your aquarium so sunlight doesn't hit it or block the sunlight. Remove uneaten food immediately and the same with dead plants. If you are doing less than 25% water changes weekly, step it up and try doing more.
You can also add some live plants to the aquarium as they compete with the algae for the same food. You just have to make sure they stay alive and healthy.
Even with these methods you might still have to scrape off the algae you already have. You can either use a razor blade for stubborn stuff or a scrub pad. Do a water change after you scrub off the stuff and do the preventative things I mentioned and algae should become less of a problem.