Lime deposits, water stains and salt creep are all the same thing: the white mineral residue left over when aquarium water evaporates. These stains consist of calcium, various bicarbonates and sodium salt. Regardless of their exact composition, removing these stains takes the same steps.
Apply vinegar to your cleaning rag. Do not apply vinegar to the stains directly, since it can drip down into the aquarium water.
Wipe down all above-water surfaces with the vinegar-soaked rag. This will remove most water stains.
With a dry rag, wipe off vinegar residue to avoid it getting in the aquarium. If you're cleaning a lid or other detachable equipment, rinse it with water to avoid vinegar dripping into the aquarium.
Scrape stubborn mineral stains with an algae scraper. You can use the algae scraper on mineral stains below the water line as long as you thoroughly rinse the tool free of vinegar before working under the water line.
Scrape any stains below the water level with an algae scraper. Most water stains will occur above the water line; but between evaporation and top-offs, some can accumulate just under the water line. Just scrape along the glass with the scraper, as you would algae. Don't worry about these minerals getting into the water; they were there in the first place and won't harm most fish.
- Wipe down the tank daily; this keeps the deposits manageable. It's harder to clean off a week's worth of calcium than it is to clean off a day's worth.
- Use cleaning products and vinegar only on the outside of an active aquarium. These can alter water chemistry.
- Make sure you use a fresh cleaning rag that has never been used with other cleaning chemicals. Many cleaning products contain chlorine or other toxic residues that can kill fish.
- Do not use household cleaning products on aquariums. Use only vinegar or aquarium cleaning products purchased from a pet shop.