Hard water is safe to drink and the preferred habitat for certain fish; unfortunately, it isn't so great for fish tanks. If you've ever noticed a white residue forming on the top of your glass tank, you're probably dealing with hard water. The residue is likely a lime buildup on the glass. As the mineral-rich hard water evaporates, it leaves behind the minerals which adhere to the glass, leaving the ugly white residue behind.
If you live in a house with hard water you likely have the same kind of build up around your shower head. While this residue won't hurt your fish, it can make them hard to see and isn't pleasant to look at.
Products to Safely Remove Lime Buildup from Glass
Lime buildup looks so terrible that there can be a great temptation to use home cleaning products to remove it. However, resist that urge, as even the smallest residue can be lethal to fish. This goes for the outside of the tank as well. There are products, such as safe aquarium cleaner, that are made to remove lime buildup on aquarium glass. Check your local pet store for fish safe cleaning sprays.
If you're looking for a greener and more inexpensive alternative, try plain white vinegar. Not only is vinegar a natural disinfectant, it also dissolves those stubborn lime deposits. For this method of cleaning, you will need to relocate your fish to a holding tank.
Once your fish have been safely removed, drain the tank completely and remove any plants or decoration. Lay the tank down on a towel, and pour enough vinegar on the affected glass to cover it. Leave it to sit for 10 to 20 minutes, then scrub with a non-abrasive pad or cloth.
If you have a really stubborn patch of build-up, try using a razor blade or algae scraper to gently scrape it away.
Do not use a razor on a plexiglass or other types of acrylic tanks as it can easily scratch them. Once you're done, rinse the tank thoroughly before refilling it. You may have to repeat the process a couple of times for each side to get it all off. This process does take a while so it's a good time to sterilize your aquarium rocks or gravel by boiling them while you wait for the vinegar to do its job.
Preventing Lime Buildups in Aquariums
The easiest way to avoid spending time scrubbing your tank with vinegar is to prevent it from getting that way in the first place. As the evaporation process is what causes the residue, keep an eye on your tanks water line. As the water starts to evaporate, replace it with distilled water. While you can and should use hard water to fill the tanks of certain fish, replacing evaporated water with more hard water can lead to a possibly lethal level of some minerals. Using distilled water eliminates the problem without adding a new one.