Water Treatment & Quality
A complete guide to water quality for discus: ideal parameters (pH, TDS, temperature, nitrite), reverse osmosis, remineralization, RO/tap mixing and dechlorination.
Discus water parameters: a complete table of ideal values
The ideal water parameters for discus — a complete table with optimal values (29°C/84°F, pH 6.0–6.8, TDS 100–200 ppm, KH 2–5, GH 3–8) and…
How to test discus aquarium water: liquid kits vs strips
How to test the water for discus — a complete guide with 5 methods (API/JBL/Sera liquid kits, quick strips, a TDS meter, an electronic pH…
The ideal temperature for discus: 29°C (84°F) and why it matters
The ideal temperature for discus — 28–30°C (82–86°F) for keeping, 30–31°C for breeding, 31–32°C for disease recovery. A guide to heaters…
The ideal pH for discus: 6.0–6.8 and how to keep it stable
The ideal pH for discus is 6.0–6.8 (5.5–7.5 acceptable for farm-raised strains). How to lower it with peat/RO/catappa, avoid a pH crash,…
TDS values for discus: 100–200 ppm for keeping, 50–100 ppm for breeding
TDS measures the dissolved minerals in your water. For discus: 100–200 ppm for keeping, 50–100 ppm for breeding. How to measure, control it…
KH and GH for discus: water hardness (anti pH crash)
KH stabilizes pH (anti pH crash); GH supports the fish's osmoregulation. For discus: 2–5 dKH and 3–8 dGH. How to measure and adjust with…
Ammonia and nitrite for discus: 0 ppm required (emergency protocol)
Ammonia (NH₃) and nitrite (NO₂) must read 0 ppm for discus. Any positive reading is an emergency. Causes, symptoms and a step-by-step…
How often to change discus water: a frequency and technique guide
Discus water-change frequency varies: 25–30% × 2/week as standard, 50% × 3/week for fast growth, 25% daily for fry. A complete guide with…
Dechlorinating water for discus: products, dosing and mistakes
A dechlorinator is mandatory for tap water (chloramine is stable and doesn't evaporate). A guide to Seachem Prime, Tetra AquaSafe and JBL…
Reverse osmosis (RO) for discus: a complete system guide
Reverse osmosis for discus — when you really need it (hard tap water, breeding, wild fish), how the system works, how to choose and install…
Mixing RO + tap water for discus: ratios and TDS calculation
Blending RO with tap water is the most practical way to give discus stable, soft-enough water. Here's the simple formula, a ratio table by…
RO water remineralization for discus: recipes and products
Pure RO water (TDS 0) is lethal without remineralization. A practical guide to Seachem Equilibrium, baking soda and Salty Shrimp Discus…
Blackwater for discus: catappa leaves, peat and tannins
Blackwater recreates the Amazon biotope — amber color, humic acids, pH 5.5–6.5. A guide to catappa leaves, peat and alder cones, with…
CO2 in a discus aquarium: yes or no + a complete system guide
Is injected CO2 compatible with discus? The honest answer: possible, but not necessary. A complete guide to the benefits, risks (pH crash,…
Frequently Asked Questions — Water Parameters
Quick answers to the most common questions about this category
Water parameters
Which water parameters are critical for discus?
Temperature 29–30°C, ammonia 0 ppm, nitrite 0 ppm, nitrate below 20 ppm, pH 6.0–7.5 (stability > exact value). KH ≥2 dKH (avoid pH crash). GH 3–8 dGH.
Read the full guideWhy must the temperature be 29–30°C and not 26°C?
Below 28°C the discus immune system collapses → Hexamita (internal parasites) and Ich (white spot) within 1–2 weeks. The high temperature is the definition of the species, not optional.
Read the full guideHow do I test the water and how often?
A liquid kit is mandatory (API Master Test Kit or JBL Test, NOT strips — ±20% error). Test ammonia + nitrite daily during cycling, then weekly. KH/GH monthly.
Read the full guideIs tap water good for discus?
Yes in about 80% of cases, but always test your own supply first — tap water varies enormously by region. A dechlorinator is mandatory (chloramine does NOT evaporate). Hard tap water (TDS 400+) → a 40-50% RO mix is recommended; soft tap water (TDS under 250) is often fine directly. Always dechlorinate (Seachem Prime).
Read the full guideDo I need an RO system at home?
It depends on your tap water. Very hard supply (TDS 400+) → YES, a home RO unit usually pays for itself within 3-6 months. Moderately soft supply → buying RO water by the bottle is often cheaper. For breeding → effectively MANDATORY. A small hobbyist with one tank → buy RO water rather than installing a unit.
Read the full guideWhat do I do with pure RO water? Is it good directly?
NO! Pure RO water (TDS 0, KH 0) = guaranteed pH crash. Mandatory: mix it with tap water (50/50 Bucharest) OR remineralize with Seachem Equilibrium + baking soda. RO water with no minerals = death within 24h.
Read the full guideWhat is a pH crash and how do I avoid it?
A sudden drop >1.0 pH within a few hours, fatal in 24–48h. It happens when KH is below 1 dKH — the water no longer buffers the acids from respiration. Prevention: KH minimum 2 dKH AT ALL TIMES, monthly testing, baking soda on hand (0.5g/10L = +1 dKH). 100% unmineralized RO water = the #1 cause.
Read the full guideHow do I lower the pH from 7.5 to 6.5 without stressing the fish?
3 safe methods: 1) RO water mixed 50/50 with tap (Bucharest) — the most stable. 2) Aquarium peat in the filter (JBL Tormec ~50g/100L) — lowers it gradually 0.3–0.8. 3) Catappa leaves + mopani wood — a 0.2–0.5 drop. Do NOT use chemical 'pH down' — it causes shocks and a pH crash when you stop.
Read the full guideI have NH₃ 0.5 ppm — what do I do NOW?
EMERGENCY: 1) 50% water change immediately with dechlorinated water at 29°C. 2) Seachem Prime double dose (5ml/100L) — neutralizes NH₃+NO₂ for 24-48h. 3) Turn on extra aeration. 4) Stop feeding for 48h. 5) Test again in 2 hours. Causes: filter cleaned in tap water, overpopulation, incomplete cycling.
Read the full guideWhat is the ideal TDS and how do I measure it?
Keeping Stendker/locals: 100–200 ppm. Breeding: 50–100 ppm. Wild (Heckel, Altum): below 50 ppm. Measure with a digital TDS meter (HM Digital TDS-3 ~60 RON, reliable for 3-5 years). Calibrate 1×/year with 342 ppm solution. Strips do NOT measure TDS correctly.
Read the full guideCan I use injected CO2 with discus?
Yes, but only for advanced keepers (NOT beginners). Strict rules: KH minimum 3–4 dKH, a solenoid on a timer (off at night), extra aeration at night, weekly pH monitoring. A complete JBL/Aquario system 300-500 €. For 90% of keepers: low-tech without CO2 is the correct choice with Anubias/Java Fern/Echinodorus plants.
Read the full guideDaily routine
How often should I change the water?
2–3 changes/week, 25–30% each. For fry: 50% daily. Don't change all the water at once. Use dechlorinated water at the aquarium temperature ±1°C.
Read the full guideHow many times a day do I feed discus?
Adults: 2 meals/day. Juveniles (under 10 cm): 3 meals/day. Fry: 4–5 meals/day. The 3-minute rule — as much as they eat without it falling to the bottom. One fasting day per week is recommended.
Read the full guideWhat do I feed discus at the start?
Beginners: premium discus pellets (Sera Discus, Tetra Discus) + frozen brine shrimp + frozen bloodworms. Avoid live food (parasite risk) and homemade beef heart in the first year (complicated).
Read the full guideMy discus refuse food — what do I do?
The first 3 days after bringing them home = NORMAL. Over 5 days = a problem. Check: temperature 29°C? ammonia/nitrite = 0? bullying? Change the type of food, try frozen. Don't insist with large amounts.
Read the full guide