When I clean up any tanks of mine I use a clean rag and white spirits. This I have found to be the most effective thing for cleaning stubborn glass stains of nearly any kind. As it is alcohol based it evaporates dry and doesn't leave smudges. Once I have cleaned the whole tank I let it sit for about 1/2 hour then give it another go for good measure. Once the white spirits has fully evaporated I then rinse it. To do this I completely fill it with water then let it sit for 1/2 hour and pour it out, I then repeat the process about 2-3 more times although once should be enough. I have never had any drama's with fish or plants by doing things this way and have been doing this for quite a while. I also use it for cleaning the outside of all my tanks and it cleans the calcium build up on the outside of one of my tanks that gets built up really my bad quicker and better than anything else that I have tried. Hope this helps.