RO water remineralization for discus: recipes and products

In short

• Pure RO is LETHAL for discus (TDS 0, KH 0, GH 0 → a guaranteed pH crash).
• Keeping: Seachem Equilibrium (≈1 g/10 L → +3 dGH) + baking soda (≈0.5 g/10 L → +1 dKH).
• Breeding: Salty Shrimp Discus Mineral GH+ (≈0.5 g/10 L → TDS ~70, GH ~3, Amazon-style minerals).
• Keeping target: TDS 100–200, GH 3–5, KH 2–4, pH 6.8–7.2.
• Breeding target: TDS 70–100, GH 2–4, KH 1–2, pH 6.0–6.5.
• Always test TDS + KH + GH after remineralizing.

What you'll learn

Reverse-osmosis (RO) water strips out 95–99% of dissolved minerals, leaving TDS near zero — a perfect base, but lethal on its own for discus. With no minerals, the pH collapses (a "pH crash"), filter bacteria struggle, and the fish's osmoregulation fails. This guide gives you exact recipes, a comparison of widely available remineralizers, and how to avoid the mistakes that lead to unstable water. For background, see reverse osmosis for discus.

Why you remineralize

⚠️ pH crash: at KH 0, the CO₂ the fish exhale overnight acidifies the water fast (pH can drop below 5.0 within ~12h) → death likely within 24h.

Choosing a remineralizer

Option 1: Seachem Equilibrium + baking soda ⭐⭐⭐⭐⭐ (recommended)

For: standard keeping of adult discus + growing juveniles.

Result: TDS ~80–100, GH ~3, KH ~2, pH ~6.8.

Pros:

• ✅ The most widely used approach in the international community
• ✅ Calcium and magnesium in a good ratio for discus
• ✅ Contains potassium (K) for plants
• ✅ Low cost per liter

Cons:

• ⚠️ No dechlorinator — add it together with dechlorinated water
• ⚠️ Baking soda must be weighed precisely

Option 2: Salty Shrimp Discus Mineral GH+ ⭐⭐⭐⭐⭐

For: serious breeding + wild types (Heckel, Altum) + professional keepers.

Composition: Ca, Mg, K, Na and trace elements modeled on Amazon river water.

Pros:

• ✅ A composition designed for an Amazon biotope
• ✅ Compatible with blackwater (catappa leaves)
• ✅ Used by many top breeders
• ✅ Naturally low TDS

Cons:

• ⚠️ Pricier than Equilibrium
• ⚠️ Availability can be limited in some regions

Option 3: Sera Mineral Salt ⭐⭐⭐

For: the average hobbyist on a tighter budget.

Pros: widely available. Cons: less discus-specific than Equilibrium.

Complete recipes by scenario

🟢 Adult keeping (target: TDS 150, GH 3, KH 2)

For 50 L (≈13 US gal) of RO water:

1. Add 5 g Seachem Equilibrium
2. Add 2.5 g baking soda
3. Stir for 2 minutes
4. Add a dechlorinator (e.g. Seachem Prime, ~1.25 ml)
5. Run an air pump for 30 minutes
6. Test TDS + KH before adding to the tank

🟡 RO + tap blend (target: TDS ~200)

For 50 L (≈13 US gal) final, with hard tap (~400 ppm):

1. ~22 L RO water (TDS 0)
2. ~28 L tap water (TDS ~400) → ~225 ppm from the blend
3. No remineralizer needed — the tap brings enough minerals
4. Add a dechlorinator only (~1.25 ml)
5. Stir 30 sec, run the air pump

🔴 Breeding (target: TDS 80, GH 2, KH 1)

For 50 L (≈13 US gal) of RO water:

1. Add 2.5 g Salty Shrimp Discus Mineral GH+
2. Add 1.5 g baking soda for a minimum KH 1
3. Stir for 5 minutes
4. Add 2 catappa (Indian almond) leaves (humic acids)
5. Add a dechlorinator (~1.25 ml)
6. Run the air pump for 1 hour
7. Test TDS + KH + GH before the change

🐣 Fry 0–3 months (target: TDS 100, GH 3, KH 2)

For 50 L (≈13 US gal) of RO water:

1. Add 5 g Salty Shrimp OR 5 g Equilibrium
2. Add 2 g baking soda for KH ~1.5
3. Add a vitamin supplement (e.g. JBL Atvitol, ~3 ml)
4. Add a dechlorinator (~1.25 ml)
5. Test — fry are the most sensitive

How to measure — correctly

A precise scale

• Recommended: a 0.1 g digital scale
• The amounts are small — 0.5 g vs 1 g makes a real difference
• Don't use "a spoonful" — that's a ±30% swing

Post-remineralization testing

1. TDS meter: check the final TDS (target ±10 ppm)
2. Liquid KH test (API, JBL): target 1–3 dKH
3. Liquid GH test: target 2–5 dGH
4. pH: let it stabilize 30 min before reading

Remineralizing — step by step

1. Prepare a separate container (a 20 L+ / 5 US gal+ bucket)
2. Pour in RO water at room temperature
3. Weigh the Equilibrium/Salty Shrimp + baking soda (separately)
4. Add the Equilibrium first, stir 2 min (it dissolves slowly)
5. Add the baking soda, stir 1 min
6. Run an air pump for 30 min (full dissolution + oxygenation)
7. Add a dechlorinator (e.g. Seachem Prime)
8. Heat to ~29°C / 84°F
9. Test TDS + KH + GH + pH before the water change
10. Add slowly (5–10 min) to the tank

Common mistakes

❌ "More is better" → GH over ~10 dGH stresses discus ❌ Too much baking soda → pH climbs above 7.5 → more toxic ammonia ❌ Table salt (NaCl) as a "remineralizer" → harmful long-term, adds no real minerals ❌ Calcium chloride (CaCl₂) alone → raises GH but not Mg → imbalance ❌ Dosing straight into the tank → local swings, stressed fish ❌ No post-remineralization test → uncontrolled variation ❌ "Top it up again tomorrow" → chronic instability

Crushed coral / aragonite — a caution

Keepers often suggest "crushed coral in the filter" for KH. For discus this isn't recommended — it releases KH but also pushes pH above ~7.8 and raises GH too much. It's fine for African cichlids, not for Amazon fish.

Blackwater + remineralization

For a blackwater biotope (catappa leaves, peat):

1. Remineralize moderately (about 50% of the normal dose)
2. Keep KH at a minimum of ~1.5 dKH (humic acids lower KH)
3. Test pH weekly — it can drop below 6.0

See Blackwater for discus.

A note on cost

Remineralizing is very cheap per liter — a single container of remineralizer typically lasts 6–12 months for a home setup. Exact prices vary by country and brand, so compare locally. (Any specific figures in our Romanian guides are Romania estimates and won't match your region.)

Remineralization checklist

• ☐ A 0.1 g digital scale
• ☐ Seachem Equilibrium OR Salty Shrimp Discus Mineral
• ☐ Baking soda (food-grade NaHCO₃)
• ☐ A calibrated TDS meter
• ☐ Liquid KH + GH tests
• ☐ A separate 20 L+ (5 US gal+) container for prep
• ☐ An air pump for oxygenation/dissolution
• ☐ Your target parameters written down (kept by the tank)

What to do next

📚 Learn more:

• Mixing RO + tap water
• Reverse osmosis (RO)
• KH and GH for discus
• Blackwater for discus

🛒 Buy:

• Verified breeders and trusted stores for remineralizers, baking soda, TDS meters and liquid KH/GH tests.