Planted Tank Calculators

Plants add beauty and a second set of needs

A planted tank is a balance between light, nutrients, carbon dioxide and fish. Plants take up ammonia and nitrate and compete with algae, but they only thrive if they get enough of what they need, and in the wrong balance the same conditions favor algae. The tools on this page cover composition, CO2 and fertilizer, which are the three areas where planted-tank keepers most often go wrong.

Which calculator answers which question

• Where do I place the focal piece? The Aquascape Hardscape Ratio Calculator applies the rule of thirds and the golden ratio to your tank.
• How much CO2 do I have? The CO2 Injection Rate Calculator gives a starting bubble rate and the pH, KH and CO2 check.
• How much fertilizer? The Fertilizer Dosing Calculator (EI) scales the Estimative Index doses to your tank.

Composition: thirds and the golden ratio

Aquascapers often place a main stone or piece of driftwood off-center, at a third of the way across the tank, or at the golden ratio of about 0.618 of the length. The calculator scales both to the length and height of your glass, so you have measurements to work from. They are guides, not laws, and a layout that looks right to you is the one to keep.

CO2: measure, don't guess

Dissolved CO2 in ppm can be estimated from pH and KH with the standard formula: CO2 equals 3 times the KH times 10 raised to the power of 7 minus the pH. Many planted-tank keepers aim for about 20 to 30 ppm, and the calculator shows a bubble-rate starting point and checks the real figure. Bubble count is only a starting point, because it depends on the regulator, the diffuser and the tank. Fish safety comes first: raise CO2 gradually, make sure the tank has surface movement for oxygen and cut the dose if fish gasp or hang at the surface.

Fertilizer: the Estimative Index

The Estimative Index method, developed by Tom Barr, doses nutrients on a schedule that is somewhat above what plants will use, and then resets any build-up with a large weekly water change, often about half the tank. The point of the method is the weekly reset, not the exact dose, and it avoids testing for each nutrient. The calculator scales common base ratios to your tank size. Fertilizer in an unplanted or lightly planted tank feeds algae, so match dosing to plant mass and light.

Light, plants and algae

Light is the engine of a planted tank, and too much light for the plants, CO2 and nutrients you have is the most common cause of algae. Start with easy, low-light plants, keep light periods modest and raise light only when plants are growing well. The Algae Troubleshooter can help you tell what you are seeing and what to change.

Common mistakes

• Buying demanding plants before the light is right. Easy plants forgive mistakes.
• Raising CO2 quickly. Fish can be harmed.
• Dosing fertilizer without enough plants. Algae gets the benefit.
• Skipping the water change. The EI method depends on it.