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 heavy amounts of nutrients in a sparsely planted tank seeds instability. If algae spores are introduced or triggered, heavy nutrients will escalate problems. On the other hand, if one has a tank full of hungry plants and do not dose enough nutrients, plants can starve & deteriorate, and this triggers algae issues as well. That being said plants are generally flexible and can grow across a wide range of nutrient levels. Comprehensive but lean dosing regimes just means that the plants grow at a slower rate -  and this is the approach we would usually suggest to beginners because it is easier to control.

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

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

Estimative Index

EI dosages are very high - designed to give non-limiting growth for most standard planted tanks. The underlying philosophy is that when plants grow well (if all their nutrient needs are met), they out-complete algae in the tank. While guessing the exact requirements of each setup is difficult, EI chooses to dose everything in excess, and resetting the levels through a large water change (50%) at end of the week. However, if you dose very richly in a sparsely planted tank, it just invites instability.

ADA

The ADA (Aqua Design Amano) line of liquid fertilizers are designed to be used in tandem with its rich substrate system, ADA aquasoil. The liquid dosing part is much leaner because the substrate contributes so much weight, nutrient-wise. Fish load can also contribute significantly to the nutrient load of a planted tank. For lean dosing systems, dosing must be done regularly to prevent nutrients from bottoming out completely.

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

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

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

Very quickly we see that the dosing numbers for EI and ADA are hugely different. Yet, we can see very successful planted tanks growth on either system.

Examples of tanks on ADA method

The tank below is grown using the ADA approach (APT Zero). EI users will be surprised how well plants grow on a leaner nutrient cycle. Lower plant mass scapes such as Iwagumis or nature style scapes with many slow growers such as Anubias and Java ferns are especially suited to this style of dosing. Slower growth and lower maintenance means that it is easier for many aquarists to achieve tank stability, which makes this one of the most popular commercial methods to easily achieve success.

The rich ADA aquasoil substrate feeds hungry rooted plants, enabling one to dose fertilizers less heavily into the water column. This is the cleanest method to run a Iwagumi tank with simple carpet - where dosing heavy nutrients into the water column with low plant loads just cause unnecessary instability & algae. Many technical aquascapers have heavy hardscape work, but light planting, so this method is popular among the competition scaping crowd as well.

Examples of tanks on the EI method

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

This is the fastest method to get a tank dense, but we find that many aquarists struggle with keeping up with the 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 which design their aquascapes in way that require plants to line up at a certain height level will find it easier to maintain the look without plants growing so quickly.

OK, what path should I take?

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

Generally, we prefer a leaner dosing approach, which gives less pruning work and give better tank stability. Low nitrates also brings out reds in certain plants better. We choose somewhat of a middle ground for most of our tanks: see table below. We would dose at lower end of the range if we were growing just an Iwagumi with smaller carpeting plants, and dose 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 aside from areas that require cosmetic sand. Plants simply grow better and more stable in soil compared to plain sand or gravel. Nutrients from the substrate zone can also be drawn upon by hungry species on a lean dosing regime.

This approach forms the basis of the Capstone formula at the heart of 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 less pruning & maintenance; this is the universal weak point for inexperienced aquarists. Growing plants is easy, but many folks will skimp on trimming to the extent that over-crowding crashes their tank. This leads to boom-bust cycles: the aquarist procrastinates from trimming as long as possible, and when they do trim, the plants are already in a poorer state of health due to over-crowding. This instability in maintenance then leads to persistent algae issues or only brief moments of stability where the tank looks good before becoming over-crowded again.

Having plants grow at a more even, slow, pace is great for overall tank stability and is tremendously useful for maintaining the same look for technical aquascapes that require plants remain at a certain height or area.

Does the richer dosing approach give richer plant colors ? 

This is another long held myth in this hobby - that the higher the level of nutrients, the redder or more colorful plants will be. There are many species that actually turn much redder when Nitrate levels in the tank are low, and these species will never be particularly red in a tank dosed with the EI approach. To read more on what affects plant coloration, read here. To learn know about which species do better in which style of tank, read 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)