The ADA dosing approach is one of many commercial systems available, but it's very commonly used and stand in stark contrast to the EI dosing approach because of the nutrient levels used - much much lower. It forms a good comparison to the EI system because we can find many successful tanks that are run on either system - so the variables and outcomes are well known and can be easily compared. Many commercial systems lie between ADA's approach (which is very lean where water column dosing is concerned) and the EI dosing approach (which doses more heavily than any commercial system).
So studying them both approaches gives a sense of the range of which tanks can run in. Some tanks run better with one approach than the other.
Lean Water + Rich Substrate
The ADA system relies on a rich substrate as a base, while the amount of nutrients dosed into the water column is far more lean. The water column dosage is high in potassium and contains iron, but contains much smaller amounts of NO3/PO4. Many of such tanks will measure 0 ppm NO3 in their water column when water is tested. Plants will mainly draw their nitrogen supply from the ammonia rich soil. As the soil pewters out (6-12months), such tanks become naturally nitrogen limited and growth slows down (may not be a bad thing). Additional new soil & root tabs are added to enrich the soil as it ages.
The lean dosing system is rooted in Asian principles that aim at reducing excess, with the idea that while higher NO3/PO4/Fe levels alone are seldom a trigger for algae (whose main trigger are organic waste/debris, unhealthy plants, excessive light etc), it can indeed exacerbate existing algae issues. Potassium has no effect on algae even at high levels, hence the system takes liberty with dosing it.
A weekly cumulative dose of nutrients using ADA's liquid fertilization system1 would give approximately: NO3 - up to 0.7ppm mix of NO3/NH3 PO4 - up to 0.6ppm K - up to 25ppm Fe/traces - up to 0.06 ppm
The decimals have been checked and there is no error. According to the above, EI's rate of dosing NO3 into the water column is about 28 times the dosage of ADA's system. This is partly due to the very rich substrate ADA aquasoil provides as a counter balance to the lean dosing in the water column.
Having a very lean water column makes it easier to maintain algae free tanks in tanks that are sparsely planted. This is why hardscape focused, sparsely planted tanks use in Aquascaping competitions do well under this regime. It is also an easy path for beginners. Growth is slower compared to tanks that run rich water column fertilization, but the tanks generally are much more stable. This methodology has proven successful enough that ADA has become one of the largest brands in the planted tank world.
Through substrate feeding, each plant has access to nutrients in its own plot of soil, whereas water column nutrients are free for all. The aggressive, faster growers will snatch up what they can when they can.
The downsides of being so reliant on substrate fertilization are costs (large volumes of aquasoil become very costly quickly), and the need to manage and enrich the soil over time.
A point to note is that the success of ADA tanks as a whole is not because of their nutrient dosing approach. (which is not particularly sophisticated) It is mostly due to their tip-top maintenance routine ; regular water changes, cleaning and siphoning of detritus, and husbandry skill to trim and position plants correctly. ADA tanks generally also choose easy growing plants that grow well in a large range of conditions; many of their tanks feature java fern and anubias, cryptocoryne species. The usage of easy plants coupled with good design results in tanks that are aesthetically pleasing yet easy to maintain.
SUMMARY OF PROS AND CONS
The reliance on rich substrate means less time and effort juggling water dosing/water parameters.
Water dosing can be reduced greatly, both in frequency and amount. Less heavy water column dosing means less issues with certain algae types such as green dust and green spot algae on hardscape/glass.
Easy method for newer aquarists as this approach require less sophistication on managing water column fertilization.
Nitrogen limited tanks give deeper reds for certain plant species (Rotala rotundifolia, Ludwigia arcuata, Limnophila aromatica etc)
Controlled growth rates may make plant arrangement easier for aquascaping purposes.
Substrate depletes over time, and requires management/enrichment.
Very lean water column means non-rooted plants may not grow as robust.
If conditions are too lean, unhealthy plants give rise to algae issues. Many aquarists may not be experienced enough to spot deficiency issues until it manifests as something serious such as a large algae outbreak.
Certain species respond well to higher amount of nutrients in the water column and do less well in such setups.
Plants become very sensitive/vulnerable to root zone disturbances.
Should I use the ADA approach to dosing?
Tanks that are suitable for the ADA dosing approach:
Planted tanks that are hardscape heavy while being sparsely planted benefit from leaner water column.
Your priority is to keep hardscape and glass free of algae.
Tank consists of plants that are able to take nitrate limitation / lean dosing; slower growers and easier species.
Red plants that color up well with nitrate limitation.
Iwagumi tanks do especially well with this approach.
Non-CO2 injected low tech tanks with easy plants.
If you want to slow down growth rates for easily maintenance.
Tanks that will probably do better on a richer dosing approach:
If you keep more difficult species that do better with more nutrients in the water column.
If you want to grow/propagate plants faster.
If you do not want to spend effort handling substrate enrichment.
If you have consistent nutrient deficiency issues; plants have thin stems, small leaves.