Water Chemistry Simplified
Think of the water as the "air" your fish breathe. If the chemistry is right, everything else follows.
The Golden Rule
In fishkeeping, Stability is more important than "Perfect" numbers. Most fish can adapt to a wide range of pH or Hardness, but they will get sick if those numbers swing wildly every day.
Toxic
Ammonia (NH₃)
Aim for: 0 ppm
Analogy: The Poison
Produced by waste. Even detectable amounts burn fish gills. Bacteria must eat this instantly in a cycled tank.
Any detectable amount (≥0.25 ppm) requires an immediate 50% water change to protect livestock gills.
Toxic
Nitrite (NO₂⁻)
Aim for: 0 ppm
Analogy: The Suffocator
Prevents fish blood from carrying oxygen. Small amounts are fatal very quickly.
If you see even 0.25 ppm, perform an immediate 50% water change to prevent suffocation.
Safe-ish
Nitrate (NO₃⁻)
Aim for: 5–40 ppm
Analogy: The Leftovers
Final stage. Less toxic. Plants love it! Keep under 40ppm via water changes.
If it reaches 80+ ppm, do a 50% water change to reset the levels to 40 ppm.
Essential
KH (Carbonate Hardness)
Aim for: ~5 dKH
Analogy: The Shock Absorber
Prevents pH crashes. Think of it as a shield that protects your water from becoming acidic suddenly.
Essential
GH (General Hardness)
Aim for: ~10 dGH
Analogy: The Vitamins
Measures Calcium/Magnesium. Essential for fish bones and shrimp shells.
Essential
pH Level
Aim for: 6.5 – 7.5
Analogy: The Acid Balance
Stability is key here. As long as it stays steady, most fish will thrive.
💧 Water Change Strategy
Water changes work by direct percentage reduction. To cut toxins in half, you must change half the water. However, the amount you change depends on your tank's specific bioload.
10–20% (Maintenance)
Weekly or Bi-weekly
- Low bioload tanks (Shrimp only, few fish).
- Heavily planted "Jungle" tanks.
- Nitrates stay consistently below 20 ppm.
- Replenishing trace minerals without shocking the system.
50% (Correction)
As needed
- Ammonia/Nitrite is detected (0.25–0.50 ppm).
- Nitrate is approaching 40–80 ppm.
- High-bioload maintenance (Goldfish, large Cichlids).
70–80% (Emergency)
Immediate action
- Toxins hit the lethal zone (Ammonia > 1.0 ppm).
- Contamination (Soap, aerosols, perfumes).
- Fish are gasping or acting highly erratic.
- After a full course of Medication.
🌍 Every Tank is its Own World
No two aquariums are the same. A 40-liter tank with two goldfish needs much more aggressive changes than a 40-liter tank with 100 plants and 5 shrimp.
Don't just follow a calendar; follow your test kit.
By testing weekly for a month, you will see how fast your nitrates rise. This lets you find your tank's unique "rhythm" and decide if you need to change 10% every two weeks or 50% every week.
⚠️ Pro Tip: Large water changes (>50%) are safe only if you match the temperature and dechlorinate properly. If you are unsure, two 30% changes over two days is safer than one 80% change.
Increasing pH / KH / GH
Crushed Coral (Slow Release): Place in a mesh bag inside your filter. This is the safest method because it dissolves slowly over weeks, preventing sudden pH swings.
Limestone/Seiryu Rock: These rocks naturally leach minerals into the water column over time, raising GH and KH steadily.
Decreasing pH / KH / GH
Catappa Leaves (Slow Release): As they decay, they release humic acids that gently lower pH over 2-3 weeks. This is much safer than chemical "pH Down" products.
RO/DI Water: The professional standard. Mixing your tap water with Reverse Osmosis water dilutes minerals instantly and precisely.
⚠️ Avoid "The Bounce"
Using liquid "pH Up" or "pH Down" creates a chemical war with your KH. Once the liquid wears off (usually in 24 hours), the pH will bounce back to its original level, often killing sensitive fish like Shrimp or Neons.
Source & Preparation
Why Boil? Always boil botanicals to kill bacteria/pests and help them sink instantly.
- Catappa Leaves: Boil 2-3 mins. Replace every 3-4 weeks (or when only the "skeleton" remains).
- Alder Cones: Boil 2 mins. Keep in for 1 month. Very potent!
- Driftwood: Boil 1-2 hours (small) or 5+ hours (large). Lasts years.
Benefits of "Tea" Water
Tannins provide natural anti-fungal and anti-bacterial protection for your fish. They mimic the natural habitats of Bettas, Tetras, Discus..., significantly lowering stress levels and encouraging breeding behavior.
How to Remove Tannins
If you prefer crystal clear water, you can remove the "amber" tint easily:
• Seachem Purigen: The "magic" solution. Put it in your filter and the water will be clear in 24 hours.
• Activated Carbon: Absorbs color but must be replaced monthly.
• Water Changes: 20% weekly will slowly dilute the tint.
✨ The "Invisible" Danger: TDS
Total Dissolved Solids (TDS) measures *everything* in the water. While not a specific toxin, a high TDS usually means the water is getting "old." If your nitrates are low but your TDS is climbing, it's still time for a water change!