Reef Tank Parameters Beginner Guide: Target Numbers
Every new reefer eventually realises the real hobby is water chemistry, not fish-keeping. This reef tank parameters beginner guide from Gensou Aquascaping at 5 Everton Park covers the nine core parameters that define a stable reef, the target ranges, the tolerant swings and the SGD-priced test kits we recommend for SG reefers. Memorise these numbers — they are the language of the hobby, and every diagnostic conversation at a local aquarium shop starts with them.
Salinity — 1.025 SG / 35 ppt
Natural seawater sits at 35 ppt (roughly 1.025 specific gravity at 25°C). Keep within 1.024-1.026. Use a refractometer, not a swing-arm hydrometer — the latter drift 0.002 SG and kill livestock through slow creep. A good ATC refractometer runs SGD 45-80 and calibrates with 35 ppt fluid (SGD 15 a bottle). Top off evaporation with RODI only, never saltwater, to prevent salinity climbing in our humid climate.
Temperature — 25-26°C
Reef tanks in tropical SG run without heaters but always need chillers. Ambient HDB rooms hit 30-32°C, which stresses corals above 28°C sustained. A Hailea HC-300A (SGD 550-650) handles up to 300 L; larger systems use Arctica DBA-200 or Resun CL-450. Fluctuation matters as much as absolute value — keep daily swings under 1°C by running the chiller through a quality controller like Inkbird ITC-308.
pH — 8.1-8.4
Reef pH tracks with alkalinity and CO2 exposure. HDB flats with closed windows accumulate CO2 and drop pH to 7.8-7.9 at night. A CO2 scrubber on the skimmer intake (SGD 80-120 assembled) with soda lime raises pH by 0.1-0.2. Measure with a calibrated pH probe or Apex monitor. pH outside 7.8-8.5 signals a real problem; 7.95 at night is just SG CO2 reality.
Alkalinity — 8-9 dKH
Alkalinity buffers pH and feeds coral skeleton growth. Eight to nine dKH suits most mixed reefs; some SPS keepers prefer 7.5-8.0 at lower nutrient levels. Stability trumps absolute value. Test twice weekly with a Hanna Checker HI772 (SGD 150 locally) — 0.1 dKH resolution beats colour-match kits. Dose Red Sea Foundation B or BRS two-part (SGD 55/3 L) to maintain.
Calcium — 420-440 ppm
Calcium pairs with alkalinity for coral skeletal growth. Natural seawater sits around 420 ppm. Test weekly with Salifert or Red Sea Pro kits (SGD 35-55 each). Supplement alongside alkalinity with two-part dosing or a calcium reactor for large SPS-dominant systems. Calcium drifting down usually means corals are growing — a welcome sign if alk is also being consumed.
Magnesium — 1300-1400 ppm
Magnesium keeps calcium and alkalinity in solution. Low magnesium causes supplements to precipitate as calcium carbonate on heaters, pumps and powerheads. Test monthly — it drifts slowly. Top up with Brightwell Magnesion, Red Sea Foundation C or BRS bulk magnesium salts. A 1 kg tub of BRS magnesium runs SGD 25-35 and lasts a year on a 90-gallon.
Nitrate — 2-10 ppm and Phosphate — 0.03-0.08 ppm
Contrary to old-school advice, zero is not the target. SPS and LPS need small, measurable nutrient levels for colour and growth. Hanna Checkers for nitrate (HI781) and phosphate ULR (HI774) each cost SGD 120-180 and remove human colour-matching error. Weekly testing and small adjustments via feeding, skimming or GFO keep numbers in range.
Ammonia and Nitrite — Both Zero
Once cycled, ammonia and nitrite stay at zero permanently. Any reading signals a biofilter problem — dead fish, lost media during maintenance, or overdosed carbon source. Keep a Seachem Ammonia Alert badge (SGD 12) on the tank wall for passive monitoring. Retest with a kit if the badge ever shows yellow-green.
Testing Kit Recommendations and Cadence
Minimum starter suite for SG beginners: refractometer, Red Sea Pro Multi (SGD 180-280) or individual Salifert kits for alkalinity, calcium, magnesium, nitrate and phosphate. Upgrade to Hanna Checkers once the hobby sticks — HI736 (calcium), HI772 (alkalinity), HI774 (phosphate ULR) at SGD 120-180 each. Weekly testing Sunday evenings takes 20 minutes and catches drift. A disciplined reef tank parameters beginner guide mindset turns numbers into intuition within six months.
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