I have a 3 year old fish tank,dind a waterchange and introduced new plants. I'm not sure if I added water safe treatement or not. The next day a found the water in my tank had gone cloudy. Waited a couple of days no change, did another water change 20/25% added treatment still no change. Please advise

Is the water being ogygenated ?

Tick

Is just the tank 3 years old or it has been set up with water in it for 3 years?

You need to wait 6 weeks for the water to properly cycle through if you have only just put the water in before it settles and you can add fish.

You can buy products to clear the water at aquarium or even pet stores but you still need to wait the 6 weeks.

Add live bacteria. The good bacteria will sometimes die off. Every time you do a water change, add the bacteria. It'll ensure that all the good stuff is still alive.

The best type of water treatment.. PRIME by Seachem. It's a conditioner and a stabilizer.

Does the tank have an oder?

There is a good chance the plants came with something on them too.

If your fish seem stressed out, add Fresh Water Salt to the water. The box should have directions on back for the right amount for your tank and for your stressed fish.