If you have noticed a white residue on the top of your aquarium, you are probably dealing with hard water. Here is an inexpensive and easy removal method.
How to Get Rid of Brown Algae (Diatoms) in the Fish Tank — Buce Plant
How to Get Rid of Algae in a Planted Fish Tank
What's causing this white 'powder' in my tank? - Practical Fishkeeping
Aquael
How To Clean Fish Tank Glass - White Residue & Algae Removal
How To Remove Brown Algae In Fish Tank (Proven Methods)
Common Fish Diseases: How To Avoid Them
How to get white residue off aquarium glass - Quora
3 Ways to Clean Aquarium Glass - wikiHow