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GLA Dry Fertilizer Calculators & Fertilizing Methods

Aquarium Plant Fertilizer Calculators:

Aquarium Nutrient Calculator: Fertilizer Dosing Calculator - Rotala Butterfly Nutrient Calculator

Dry Aquarium Fertilizing Methods:

Understanding Dry Aquarium Fertilizer & Planted Tank Fertilizing Methods - an informative overview of the dry fertilizer dosing methods GLA follows to achieve aquarium growth and success. Learn how, when and why to fertilize your planted tank, while understanding the methods and calculators to help you achieve your goals. We also summarize the important micro and macro nutrients to help you get started.

PPS-Classic and PPS-Pro Dosing Method (Founder) - explore everything related to PPS-Pro written by its founder, you can really dive into learning the science and relationships of PPS-Pro and your planted tank.

GLA PPS-Pro Aquarium Ferts Instructional Guide - PPS-Pro or Perpetual Preservation System is a low maintenance planted tank fertilizing method. Our GLA PPS-Pro fertilizer package includes everything you need to get started, including fertilizer mixing and dosing bottles, GLA EDTA Micromix (trace elements), Potassium Nitrate KNO3, Mono Potassium Phosphate KH2PO4, Potassium Sulfate K2SO4, and Magnesium Sulfate MgSO4. Just follow our detailed instructions to create your micros and macros fert mixtures, and dose each bottle daily, it's easy and straightforward. The ideal fertilizing method for minimal testing and tweaking, compatible with a variety of lighting and water change schedules.

Estimative Index (EI) Fertilizing Method - the estimative index or EI aquarium fertilizer method involves routine high dosing of dry micro and macro nutrients in your planted tank. Algae growth in the aquarium is controlled with the with appropriate balance of fertilizing, high lighting, and a stable CO2 supply around 30ppm. During an EI method dosing week, micros and macros are alternated daily with a 50% water change on Sunday to reset nutrient levels and remove excess in the aquarium.

How to Fertilize

There are two major Fertilizing Methods to follow – PPS (Perpetual Preservation System) and EI (Estimative Index). To properly fertilize your planted tank, you will need to research and choose a method that fits your needs and tank conditions. Always be sure to carefully observe the plant conditions in you tank to avoid over or under fertilizing.

There are several methods you can use to get the ferts in your aquarium.

  • Measure out the predetermined amount of dry ferts and place the dry fert(s) directly into the aquarium water.
  • Mix the predetermined amount with a little bit of aquarium water in a container until it dissolves, and then pour the solution into the aquarium.

A Closer Look at Micronutrients and Macronutrients

Macros / Macronutrients (NPK) – there are three major macronutrients: Nitrogen (N), Phosphorous (P), and Potassium (K).

Micros / Micronutrients / Trace Elements – the most popular include: Iron, Boron, Manganese, EDTA Micromix, Miller Microplex.

Nitrogen (N) – the most common source is Potassium Nitrate (KNO3). It is the staple nutrient of all plants. It helps plants produce enzymes, proteins, and amino acids. A lack of nitrogen halts plant growth and promotes decay.

Phosphorous (P) – the most common source is Mono Potassium Phosphate (KH2PO4). Assists in plant DNA and RNA replication, and growth related processes. A lack of Phosphorous can result in the decreased ability for plants to uptake or absorb nutrients, leading to excess nutrient in the water and potential algae conditions.

Potassium (K) – potassium is found in compounds such as KNO3 and KH2PO4. For tanks with potassium deficiencies Potassium Sulfate (K2SO4) provides the element of potassium. Potassium plays a very important role in photosynthesis optimization, while keeping plant processes and production in a constant state of activity.

Fertilizer Dosing Methods:

Fertilizer Dosing Calculator:

What you will need to get started with PPS:

  • our PPS-Pro fertilizer package
  • distilled or RO water
  • a digital scale

Preparing the PPS fertilizer mix in the 500mL bottles:

The following solution recipe is based on the use of two 500mL bottles. Before starting, we recommend to boil the plastic bottles to sanitize them.

Step 1:

Bottle #1 – use your digital scale to weigh the following ferts, then place dry contents in bottle:

  • K2SO4 – 29.3 grams
  • KNO3 – 32.6 grams
  • KH2PO4 – 2.9 grams
  • MgSO4 – 20.2 grams

Step 2:

Bottle #2 – use your digital scale to weigh the following ferts, then place dry contents in bottle:

  • GLA EDTA Micromix – 28.6 grams (Trace Elements (TE) recipe updated 4/11/2016, previous recommendation was 40 grams)

Step 3:

Fill both bottles with distilled or reverse osmosis (RO) water, up to the 500mL water level line. Screw on caps tightly and shake well. Let the mixture sit over night until dissolved completely.

How to dose the PPS mixture:

Bottle #1 Macros: daily dose of 1 mL per every 10 gallons or 40 litres of aquarium water. Dose daily, prior to your aquarium lights turning on.

Bottle #2 Micros: daily dose of 0.5 mL or 10 drops per 10 gallons or 40 litres of aquarium water. Dose daily, prior to your aquarium lights turning on. (updated 7/7/2018, previous dosing recommendation was 0.1mL or 2 drops per 10 gallons)(updated 4/11/2016, previous dosing recommendation was 1 mL per 10 gallons)

(1 ml = 20 drops)

How to do PPS-Pro with water changes:

Dose PPS-Pro Solution #1 and PPS-Pro Solution #2 at the same time daily for a week, then 50% water change.

Low light:

PPS-Pro Solution #1, 0.5ml or 10 drops per 10 gallon or 40L

PPS-Pro Solution #2, 0.25ml or 5 drops per 10 gallon or 40L

Water change 50% once a week

This limits water column nutrient levels to 7 ppm NO3, 0.7 ppm PO4, 9 ppm K, 0.7 ppm Mg, 0.35 ppm Fe(TE).

Medium light:

PPS-Pro Solution #1, 1ml per 10 gallon or 40L 

PPS-Pro Solution #2, 0.5ml per 10 gallon or 40L

Water change 50% once a week

This limits water column nutrient levels to 14 ppm NO3, 1.4 ppm PO4, 18 ppm K, 1.4 ppm Mg, 0.7 ppm Fe(TE).

High light:

PPS-Pro Solution #1, 2ml per 10 gallon or 40L

PPS-Pro Solution #2, 1ml per 10 gallon or 40L

Water change 50% once a week

This limits water column nutrient levels to 28 ppm NO3, 2.8 ppm PO4, 36 ppm K, 2.8 ppm Mg, 1.4 ppm Fe(TE).

(1 ml = 20 drops)

Estimative Index Fertilizing Method

The Estimative Index, or EI for short, is a reasonably new method of dosing fertilisers in a planted aquarium. The basic idea involves dosing more nutrients than the plants actually need, but in such a balance that algae cannot take advantage. This includes the micro as well as macronutrients, and works best for aquaria with high lighting and very dense planting.

Wait a minute. Doesn’t excess nutrients in the water column led to increased algae growth? Well no, not really. Remembering that it is an imbalance of nutrients, rather than an excess which causes algae. In order for algae to proliferate it needs other excess components such as lighting and CO2 to consume the abundance of nutrients supplied by this fertilizing method.

EI is based on the effects of high lighting and stable CO2 injection at around 30ppm. C02 saturation levels can either be checked by comparing the pH and KH readings, or by investing in a CO2 Drop Checker. The latter is far more accurate and shows real time results with color changes based on low, medium and high CO2 levels.

How does Estimative Index Work?

A standard EI schedule works around a 7-day week, which makes it easy enough to work out. On the Monday (the first day), you would add your Macros, and on the Tuesday you could safely add the Micros without the fear of losing the Iron through a reaction with the Phosphate. The dosing continues like this on alternate days, until Sunday where you would do a 50% water change. This resets the nutrient levels in the aquarium, and makes sure that the excess nutrients are removed. The cycle starts again on the Monday with the Macros. This schedule can obviously be adjusted to suit your needs, but these are the basic principles.

Powdered fertilisers are most commonly used when using the EI method because they are easy to administer.

Primary Fertilizers

The primary macro elements consists of Nitrate (found in KNO3), Phosphate (found in KH2PO4), and Potassium (found in both of these compounds as K). The other primary class of elements is lumped in what is known as micro elements which is a mixture of different minerals i.e. iron, magnesium, boron, etc.

Sometimes, but not necessarily, people will add Magnesium Sulphate (MgSO4) to help with the buffering capacity of the water (measured as KH). When using R/O water or any water with a low buffering capacity, this will aid against pH crashes overnight due to CO2 build-ups (which can sometimes form an excess of carbonic acid). Nitrates will also form nitric acid, which will try and push the pH down as well. Even with the relatively high Nitrate levels used in EI, the acidifying effect is not as noticeable as it is with CO2 injection. You can use a solenoid on a timer to turn off the CO2 supply at night which can help to keep things stable. It should be turned on again an hour or two before the lights come on again in the morning to give the CO2 levels a chance to build up again.

Proper Mixture Ratios


Having separate solutions for NO3, PO4 and Micros will allow you to alter the concentrations of each parameter, which is helpful when fighting algae or certain nutrient deficiencies.

Generally it is accepted that a ratio of 10:1 NO3 and PO4 works well, but again, it differs for each plant species used. You should look at around 20-30ppm of NO3, and so 2-3ppm of PO4. The Potassium (K) can be kept the same as NO3, and the CO2 should be kept at a constant 30ppm.

You can follow these general dosing recommendations: