APT e is 2HR Aquarist's ready-to-use take on the Estimative Index (EI) — the well-known, nutrient-rich dosing method pioneered by Tom Barr. EI gets results but is famously fiddly to mix and tune from raw salts; APT e bottles that whole approach into a single calibrated all-in-one liquid, so you get the generous, plant-driving nutrition of EI without the guesswork or the kitchen-chemistry. It carries a complete macro and micronutrient profile, including extra magnesium for stronger growth.
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: Classic EI deliberately floods the tank with nutrients, which grows plants fast but can mute the deep reds aquascapers prize and invite algae. APT e is tuned to be, in 2HR's words, "2X more nitrate limiting for richer colours" than conventional EI mixes — you keep EI's vigorous growth while pulling nitrates back enough to bring out stronger coloration and cleaner tanks. It's the richest of the APT liquid line, making it a natural fit for high-light, CO2-injected, fast-growing scapes.
If you run a demanding, high-energy planted tank and like the EI philosophy, APT e is the easiest way to do it well. And like the rest of the line it plays nicely with the others — many aquascapers mix and match APT e, APT 1, and APT 3, or pair any of them with APT Jazz in the substrate, to fine-tune nutrition to their tank.
Dosing Guidelines: A simple starting point is about 1 mL per 13 gallons, dosed daily (2HR's reference is 2 mL per 100 L). Timing during the day doesn't matter — plants store nutrients — so pick a schedule you'll keep: daily or 4+ times weekly for high-light, fast-growing tanks, or scale back for calmer setups. 2HR Aquarist offers a free online APT e dosing calculator to match the dose to your exact tank.
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