APT Sky is a remineralizer with a clever trick up its sleeve. Like any GH booster it adds the calcium, magnesium, and trace minerals — plus a touch of natural seaweed extract — that soft or RO water lacks, supplying the building blocks plants and shrimp need to thrive. What sets it apart is what it leaves alone: it raises general hardness (GH) without nudging your nitrogen, phosphorus, or potassium, and without raising KH or shifting pH. Most remineralizers quietly add extra potassium and skew the nutrient ratios your fertilizer is built around — APT Sky doesn't.
At Cuboid, the APT range is what we run in our own aquascaping display tanks — products we use ourselves day in and day out, and recommend without hesitation to anyone serious about a planted aquarium.
Why It's Different: Conventional GH boosters tend to raise hardness and your NPK at the same time, which works against a calibrated fertilizer dose. APT Sky keeps mineral content and plant nutrition as two separate dials you can tune independently. One thing to know: because it adds minerals rather than removing them, it's designed for soft or RO water — it can't soften water that is already hard.
The payoff is freedom. With GH dialed in, APT Sky lets — in 2HR Aquarist's words — "hardwater and softwater plants thrive side-by-side" in one tank, and magnesium-hungry species like Rotala macrandra finally get what they crave. It's also a real boost for shrimp: steady calcium supports healthy molting and breeding, which is why softwater shrimp keepers swear by it. Best of all, it's built to work hand-in-hand with the rest of the APT fertilizer line.
Dosing Guidelines: APT Sky is a super-soluble, non-caking powder with an easy rule of thumb: one 5 ml scoop (about 3.5 g) per 10 gallons raises GH by roughly 4 dGH, or about 71 ppm. Most planted tanks thrive around 5–7 dGH (90–125 ppm), so scale to your tank size and top up at each water change to hold levels steady. For an exact amount matched to your water, 2HR Aquarist's free online APT Sky dosing calculator does the math for you.
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