2Hr Aquarist APT SKY

Add APT SKY directly to your tank, or better, to the fresh water you use for a water change, and let it circulate. It's made of calcium and magnesium salts, which have low solubility, so it can't be concentrated into a small stock solution or added through an automatic doser. It needs a large body of water to dissolve fully. Dose to your target GH. Most planted tanks do well at around GH 6, and our our dosing calculator gives you the exact amount for your tank volume.

You need a remineraliser if you run RO/RODI water, or naturally very soft tap water that's low in GH. If your tap water is already moderately hard, you likely don't need one. Between the two: APT SKY raises GH only (calcium and magnesium) and leaves KH and pH untouched, which suits most planted tanks and soft-water, acidic-loving fish. APT SKY PLUS raises both GH and KH (and nudges pH up slightly), so choose it if your fish or shrimp need a specific, stable KH.

As a rough guide, RO water remineralised to 5–7 dGH usually sits somewhere around 85–150 TDS. But TDS isn't the best way to dose accurately. The reliable method is to dose APT SKY by weight, using an accurate weighing scale, rather than by volume or by chasing a TDS reading.

TDS only reports the total dissolved ions in your water as a single combined number. It doesn't tell you which ions are present or in what ratio, and readings shift with your meter, its calibration, and whatever is already dissolved in the tank. That makes it useful for tracking relative changes over time, such as watching TDS climb between water changes, but unreliable as an absolute target. Weighing your dose gives you a precise, repeatable result every time.