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.
Ammonia & Nitrite
What they are: The absolute worst toxins. Think of them like leaving rotting garbage
inside a sealed room. Fish breathe this in, and it burns them instantly. In a healthy tank,
invisible beneficial bacteria eat this trash constantly to keep the air clean.
Nitrate
What it is: Safe leftovers. After the bacteria finish cleaning the toxic trash
(Ammonia and Nitrite), they leave behind Nitrate. It is mostly harmless in small amounts. Think of
it as plant food (fertilizer) - your live plants eat it, and you throw away the excess whenever you
do a water change.
pH (The Flavor)
What it is: How "sour" or "sweet" the water feels to your fish. Low pH is acidic
(like lemon juice), and high pH is alkaline (like baking soda). Fish hate sudden changes to this
flavor more than anything else. Keeping it steady is much more important than hitting a exact
decimal point.
KH & GH (The Mineral Shields)
• KH (The Sponge): Chemically measures dissolved carbonates and
bicarbonates. It acts as a safety buffer that absorbs acids. Without KH, your pH can
crash overnight like a stone.
Normal Range: 4–8 dKH (approx. 70–140 ppm) for community tanks.
• GH (The Vitamins): Chemically measures dissolved calcium and magnesium
ions. Your fish and shrimp absorb these minerals directly to build strong skeletons and
hard shells.
Normal Range: 4–12 dGH (approx. 70–200 ppm) for community tanks.
TDS & RO Water
• TDS (Total Dissolved Solids): Measures absolutely everything dissolved in your
water - minerals, salts, metals, and organic waste. Think of it as a "water clutter index." Too much
clutter makes it physically harder for fish to breathe and regulate their bodies.
Normal Range: 100–300 ppm (Softwater species and sensitive Caridina shrimp require low TDS of
100–150 ppm; Neocaridina shrimp, snails, crabs, and hardwater fish prefer 150–300+
ppm).
RO, Distilled, & Bottled Water
• RO (Reverse Osmosis): Water pushed through a fine membrane that strips out 99% of
minerals, chemicals, and impurities (0 TDS). It is a completely blank slate with no buffers, meaning
you must manually add minerals back (remineralize) before using it in your tank.
• Distilled Water: Purified by boiling water into steam and condensing the vapor
back into liquid. Physically, it is identical in purity to RO water (0 TDS) and is a perfect
alternative, but it also has zero minerals and must be fully remineralized.
• The "Low Mineral" Trap: Bottled water labeled as "spring" or "low mineral" is
processed for human drinking taste, not aquariums. To a human, "low mineral" can still mean a TDS of
50–150+ ppm. Worse, these bottles often contain added minerals for flavor (like sodium or silica,
which can trigger diatom algae blooms), making them unpredictable and risky compared to true RO or
distilled water.
💧 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!