Brackish Tank Salinity Management Guide: SG 1.005 to 1.015
Salinity is the single dial that separates a thriving brackish tank from a stressed one, and most beginner failures come from guessing it rather than measuring it. This brackish tank salinity management guide from Gensou Aquascaping at 5 Everton Park covers the working range of SG 1.005 to 1.015, the difference between hydrometers and refractometers, and the slow ramping schedule needed to keep monos, scats, and puffers calm. Singapore tap water comes in soft and chloride-light, so every gram of marine salt you add is doing real work.
Quick Facts
- Working range: specific gravity 1.005 (low brackish) to 1.015 (high brackish)
- Mid-brackish target for most community species: SG 1.010
- Use marine salt mix (Red Sea, Instant Ocean, Tropic Marin), never table salt
- Refractometer is the accurate tool; swing-arm hydrometers drift 0.002-0.005
- Ramp salinity by no more than 0.001 SG per week up or down
- Calibrate refractometers monthly with 35 ppt or RO standard fluid
- Always pre-mix salt in fresh aged water, not directly into the display
Why Specific Gravity, Not Just Salinity
Specific gravity (SG) is the density of your tank water relative to pure water at a fixed temperature, and it is the unit most aquarists actually read off a refractometer or hydrometer. Pure freshwater sits at 1.000, full reef strength at 1.025-1.026, and the brackish band falls neatly in between. Quoting SG rather than ppt avoids the conversion arguments and lines up with the equipment you can buy locally for under $30.
Temperature matters. Most refractometers are calibrated for 20°C, but Singapore tanks run 26-28°C. Automatic-temperature-compensated (ATC) units handle this for you; cheap non-ATC ones need a correction chart or you will misread by 0.001-0.002.
Picking a Target For Your Stock
Different brackish species sit at different points on the spectrum. Bumblebee gobies, figure-eight puffers, and Indian glassfish do well at SG 1.005-1.008. Monos, scats, columbian shark catfish, and adult green spotted puffers prefer 1.010-1.018, drifting toward marine as they age. Mudskippers want 1.005-1.010 with land access. Pick the lowest comfortable salinity that suits every animal in the tank, then commit to it.
Hydrometer Versus Refractometer
A swing-arm hydrometer costs $8-15 and is fine as a quick sanity check, but salt residue and air bubbles drift it 0.002-0.005 over time. A handheld refractometer ($25-40 on Shopee or Carousell) is the standard tool: a few drops of tank water on the prism, hold to a light source, read the line. Wipe the prism dry after each use and store it in its case so the optics stay aligned.
Calibrate monthly. Use either a sachet of 35 ppt calibration fluid (about $5) or a known standard like RO/DI water at 1.000. Most Asian-market refractometers ship out of calibration by 0.001-0.002 and need an initial zero with the tiny screwdriver included in the box.
Mixing Marine Salt Correctly
Marine salt is sold in 4 kg buckets ($20-30) and 22 kg drums ($60-90). For a target of SG 1.010, dissolve roughly 14 g of salt per litre of fresh water; for 1.015, around 21 g per litre. These are starting points only; mix, aerate for an hour, then measure with a refractometer and adjust.
Always mix in a separate bucket with a powerhead or air pump. Dumping dry salt into the display creates burn spots on plant roots and shocks fish around the dissolution zone. The mix needs at least 30-60 minutes of agitation to fully dissolve the calcium and magnesium components.
Ramping Salinity Up Or Down
Brackish fish tolerate slow changes; they do not tolerate fast ones. If you are converting a freshwater quarantine tank into a brackish display, raise SG by no more than 0.001 per week. That looks like adding 1.4 g of salt per litre weekly to climb from 1.000 to 1.005 over five weeks.
Going the other way (acclimating wild-caught monos from full marine down to brackish, for example) follows the same 0.001 per week rule. Faster drops cause osmotic stress, white slime coat shedding, and bacterial infections within days.
Top-Up Versus Water Change Maths
Evaporation removes pure water and leaves salt behind, so SG climbs over the week. Top up with fresh dechlorinated water only — never salted water — to bring volume back to the line. Water changes use pre-mixed salt water at the same SG as the display; mismatched change water is the most common cause of accidental salinity swings.
For a 200 litre brackish tank evaporating 4-6 litres weekly in an air-conditioned HDB room, top up every 2-3 days with RO or aged tap to keep SG steady. Test before and after each change.
Singapore Sourcing Notes
Marine salt mix is stocked at most C328 Clementi, Polyart, and Y618 outlets, and refractometers turn up reliably on Carousell secondhand for $20. PUB tap water dechlorinated with Prime is fine as the freshwater base; a small RO unit ($120-200) only becomes worthwhile for high-end marine work, not standard brackish.
Common Mistakes
The big three are using table salt (no buffers, no trace minerals), trusting an old hydrometer, and changing salinity too fast. Aquarium salt sold for ich treatment is also not marine salt — read the label, look for sodium chloride content under 90% and added carbonates.
Related Reading
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