I have this salt stain round the top of the aquarium where the water has evapurated
a have tried to scrib it but there was no difference. It doesn't harm the fish but I just want to get rid of it. mabye the is some sort of chemical?
As far as I'm aware, salt does not evaporate, hence the fluctuating salinity in a saltwater tank as the water evaporates. If you are talking about this white sort of cobweb looking things on the glass of your freshwater tank, I believe these are calcium deposits.
I noticed them on my tanks, but when I try to clean them they come right off. Have you tried scrubbing both sides of the glass? If you can't get it off, don't worry about it, and aesthetic hindrance is nothing concerning your fish's well being. The only chemical I would recommend you use if you find the stains very distracting is white vinegar. Usually in most kitchens, this can be used as an aquarium safe glass cleaner. Just dab a little of it on a paper towel or something. Even though its aquarium safe, I would definitely recommend that you try not to get any into the tank water.
It's 'fur' (calcium salts) from the hard water, just like you get in a kettle.
A dilute acid solution will shift it, but it's important that none goes in your tank water.
I usualy just scrape it off with a razor or craft knife blade.
if u want to avoid it once u got it off then u might wanna get a power head or something that will make the water surface move so that even if it does get bac there it'll be disolved but the water again and i'd also advise that u jus scrub it every time u clean ur tank.