Fertilizer dosing guide for planted aquariums; when to dose more or less ?

Should I dose heavily or lightly?

This depends on the type of aquascape you have. Dosing high levels of nutrients into a sparsely planted tank will create instability. If algae spores are introduced or triggered, heavy nutrients will escalate the problems. On the other hand, if you have a tank full of hungry plants and you do not dose enough nutrients, the plants can starve and deteriorate and this will also trigger algae problems. However, plants are generally flexible and can grow over a wide range of nutrient levels. An extensive but lean dosing regime simply means that the plants will grow more slowly - and this is the approach we would normally recommend to beginners as it is easier to control.

Let us compare the methods of 2 dosing systems at opposite ends of the spectrum - the EI dosing approach (which uses high levels of water column nutrients) versus a lean dosing system, ADA (which uses lower levels of water column nutrients but rich substrate). Almost all tanks will fall somewhere in the middle of the spectrum, so by learning about both approaches you can choose how to manage your own system.

Looking at these two popular methods shows just how big the differences between dosing levels can be, and both systems can produce great planted tanks.

Estimative Index

EI dosages are very high - designed to provide unrestricted growth for most standard planted tanks. The underlying philosophy is that when plants are growing well (when all their nutrient needs are met) they will out-complete the algae in the tank. Whilst it is difficult to estimate the exact requirements of any particular set-up, EI's approach is to overdose and then reset the levels with a large water change (50%) at the end of the week. However, over-dosing in a sparsely stocked tank is an invitation to instability.

ADA

The ADA (Aqua Design Amano) liquid fertiliser range is designed to be used in conjunction with the rich substrate system, ADA aquasoil. The liquid dosing part is much leaner because the substrate contributes so much weight, nutrient wise. Fish loading can also contribute significantly to the nutrient load of a planted tank. Lean dosing systems need to be dosed regularly to prevent nutrients from building up.

The table below compares the EI approach with the ADA1 approach:

​*parts per million, which is the same as mg/L

If you are dosing 3 times a week, divide the weekly dose by 3. For example, if you were targeting ~18ppm NO3 per week (EI approach), you would dose 6ppm each time on Monday, Wednesday, Friday for a total weekly dose of 18ppm.

Very quickly we see that the dosage numbers for EI and ADA are very different. However, we can see very successful planted tank growth on both systems.

Examples of tanks on ADA method

The tank below is grown using the ADA approach (APT 1).

EI users will be surprised at how well plants grow on a leaner nutrient cycle. Low mass plants such as Iwagumis or natural style plants with many slow growing plants such as Anubias and Java ferns are particularly suited to this type of dosing. Slower growth and less maintenance means that many aquarists find it easier to achieve tank stability, making this one of the most popular commercial methods to achieve easy success.

The rich ADA Aquasoil substrate feeds hungry rooted plants, allowing less fertiliser to be added to the water column. This is the cleanest way to run an Iwagumi tank with a simple carpet - where dosing heavy nutrients into the water column with low plant loads will only cause unnecessary instability and algae. Many technical aquascapers have heavy hardscaping but light planting, so this method is also popular with the competitive aquascaping crowd.

Examples of tanks on the EI method

The EI method, pioneered by Tom Barr, is popular among North American aquascapers. For tanks with heavy plant loads, having high nutrient levels in the water column means that aggressively growing plants will not out-compete more delicate growers. Plants also grow bigger, faster and more robust due to high nutrient levels. This is also the easiest method to ensure success when growing difficult species. For specialist growers, this method produces plants quickly.

It is the fastest way to make a tank dense, but we find that many aquarists struggle to keep up with pruning and replanting cycles - because faster growth quickly leads to overcrowding and deterioration of older growth in deep shade if pruning and replanting are not done frequently. Similarly, aquascapers who design their aquascapes so that the plants line up at a certain height will find it easier to maintain the look without the plants growing so quickly.

OK, what path should I take?

We find the EI system too rich for many tanks that focus on hard foliage and have less plant mass, and we find the ADA system a little too lean (especially when the Aquasoil substrate wears out after many months).

In general, we prefer a leaner dosing approach which results in less pruning and better tank stability. Low nitrates also bring out the reds in certain plants better. For most of our tanks we choose a middle ground: see table below. We would dose at the lower end of the range if we were growing just an Iwagumi with smaller carpet plants, and higher for a dense stem plant scape such as above. We find that within the ranges below we can run any style of tank well with a relatively controlled growth rate. We also use soil-based substrates in all of our tanks, except in areas where cosmetic sand is required. Plants simply grow better and more consistently in soil than in plain sand or gravel. Nutrients from the substrate zone can also be used by hungry species on a lean dosing regime.

This approach forms the basis of the Capstone formula at the heart of APT 3 (previously called APT Complete), which is available for sale here.

A 2Hr Aquarist farm tank uses some water column dosing and a rich substrate.

What?! Why choose to grow plants more slowly ?

The main reason is a lack of pruning maintenance, which is the universal weakness of inexperienced aquarists. Growing plants is easy, but many people skimp on pruning to the point where overcrowding brings the tank to its knees. This leads to boom-bust cycles: the aquarist puts off pruning for as long as possible, and by the time they do prune, the plants are already in a poorer state of health due to overcrowding. This instability in maintenance then leads to ongoing algae problems or only brief moments of stability when the tank looks good before it becomes overcrowded again.

Having plants grow at a more even, slower pace is great for overall tank stability and is extremely useful for maintaining the same look for technical aquascapes where plants need to remain at a certain height or area.

Does the richer dosing approach give richer plant colors ? 

This is another long-standing myth in the hobby - that the higher the nutrient level, the redder or more colourful the plants will be. There are many species that actually become much redder when the nitrate level in the tank is low, and these species will never be particularly red in an EI-dosed tank. To read more on what affects plant coloration, read here. To learn know about which species do better in which style of tank, Click here.

When to choose leaner dosing approach

• Iwagumi & nature style scapes with small plants/slow growers
• You want to moderate plant growth rates, or are attempting to slow down growth rates to reduce pruning
• Stability and lower maintenance are priorities
• Tank is sparsely planted or populated with mostly slower growers
• Technical aquascapes that require plants stay at a certain height or area
• When you are growing species that require N limitation to gain color
• You have persistent algae issues, such as Green dust algae on glass or on plants

When to choose a richer dosing method 

• You have time to do frequent trimming and replanting, water changes
• You are trying to grow difficult plants and want them to grow faster
• You want faster growth rates and larger, more robust plants
• Tank has more than 50% of the substrate space planted with stem plants or large aggressive growing plants
• You know how to maintain a tank system with no significant algae triggers

¹ new Green Brighty series (after 2018)