A green residue appears to be on the bottom of my tank

Question
Hi Kim,

I am currently setting up a new tank, i purchased the tank second hand from a fish store hence it has been used before. I washed the tank up but whilst doing so i noticed some green algae looking residue at the bottom of the tank. I tried scrubbing it but it wont come off. It appears to have eaten into the glass giving it a rough surface. I just wanted to know if this is bad for the fish? or if it wont be an issue. I could take a picture of it to show you to make it clearer if you like.

Thanks
Michael

Answer
I would try using a razor blade to scrape it off. I would add a little water to help soften it first. Just be careful not to cut yourself or scratch the aquarium badly. Maybe even mix up one part white vinegar to two parts water and let it soak for awhile. Who knows what it could be in there. After the vinegar, wash the aquarium with just warm water several times until the smell of the vinegar is gone. Let it air dry, and smell it again to make sure it's gone. If you can still smell it, repeat until the smell is gone. I'm sure it probably is some form of an algae residue. It most likely won't hurt the fish either but you don't want to take a chance of there being some type of bad bacteria or a disease in it, or be adding a ton of algae to your fishes clean water when later on you will be "trying" your best to keep it "out" of there. I know myself and my snails fight very hard to keep it out of my tanks. lol
Hope this helps. Send me a follow up if you have more questions.