Water Quality Fixes
Water quality is the heart of a healthy fish tank. Even if everything looks fine on the surface, poor water conditions can lead to sick fish, algae outbreaks, and a tank that’s more work than fun. Whether your parameters are off or things just don’t look right, here are the most common water quality problems—and how to fix them.
​
1. Ammonia or Nitrite Spikes: These are usually caused by overfeeding, overcrowding, a new tank that hasn’t fully cycled, or a crashed cycle from cleaning too aggressively.
Fix it: Do an immediate 25–50% water change. Stop feeding for a day or two. Add beneficial bacteria supplements (like Seachem Stability or Tetra SafeStart). Test daily until levels go back to zero. Check if you over-cleaned your filter—never rinse media in tap water!
Pro Tip: A properly cycled tank should always read 0 ppm ammonia and 0 ppm nitrite.
​
2. High Nitrates: Nitrates naturally build up over time from fish waste and leftover food. High levels can stress fish and fuel algae growth.
Fix it: Perform regular water changes (20–30% weekly is ideal). Add live plants—they absorb nitrates naturally. Cut back on feeding and vacuum your substrate. Rinse your filter sponge to remove trapped debris (in tank water only).
Target level: Keep nitrates below 40 ppm for most tanks, or under 20 ppm for sensitive species.
​
3. Cloudy Water (White or Gray): This is often caused by a bacterial bloom (common in new tanks), overfeeding, or dirty gravel.
Fix it: Reduce feeding and do partial water changes every 2–3 days. Clean your substrate and remove uneaten food. Add a water clarifier if needed (short-term fix). Make sure your filter is appropriate for your tank size and is running 24/7.
​
4. Green Water (Algae Bloom): Caused by excess light, high nitrates, and phosphates. Often seen in tanks near a window or under strong lights.
Fix it: Reduce lighting to 6–8 hours per day and move the tank out of direct sunlight.Do small frequent water changes (don’t scrub everything—it’ll just come back faster). Use algae control products or add live plants to outcompete the algae. Test for nitrates and phosphates and adjust feeding if needed.
​
5. Low pH / High pH: Sudden changes in pH can harm or even kill fish. This is especially tricky in saltwater tanks and for species that need stable conditions.
Fix it: For low pH: Use crushed coral or a pH buffer to raise it slowly.For high pH: Use driftwood or almond leaves (for freshwater), or a pH-lowering buffer. Always change pH gradually, never more than 0.2 per day. Ideal pH varies by species—always research the needs of your fish!
​
6. Low Oxygen Levels: If your fish are gasping at the surface or lethargic, your tank might not be oxygenated enough.
Fix it: Add an air stone, bubbler, or increase surface agitation. Make sure your filter outlet disturbs the surface. Lower the temperature slightly —warmer water holds less oxygen.
​
7. Hard Water / Soft Water Issues: Some fish thrive in hard water, others in soft. If your fish look stressed and your parameters are way off, this could be the cause.
Fix it: For hard water: Use distilled or RODI water mixed with tap water. For soft water: Add crushed coral or mineral supplements. Know your source water before picking your fish!
​
8. Dirty or Smelly Water: If your tank smells bad or looks murky, you’ve likely got a mix of overfeeding, poor filtration, or missed maintenance.
Fix it: Do a large water change (40–50%) and clean the substrate. Check your filter—clean or replace media as needed. Make feeding smaller, and more consistent. Add carbon to your filter to help with odors (temporary fix).
Tools That Help Keep Water Quality in Check:
Liquid Test Kits (API, Salifert) — more accurate than strips.
Gravel Vacuum — keeps the substrate clean during water changes.
Beneficial Bacteria Bottles — help maintain or reset the cycle.
Water Conditioner — always use when adding tap water.
Algae Scraper — keeps glass clean and water looking clear.