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I tend to place planted tanks into two main divisions in FW plant keeping:
CO2 or no CO2(Carbon enriched eg "Excel" might be included here).

Then these are subdivided into fert routines.

Substrate fert's and water column ferts.

Substrate ferts make sense for non CO2 methods much more due to slow growth rates=> supply= growth RATE

Every tank has Water column ferts of one type or another(K+, GH, Fish waste, etc).
CO2 enriched tanks make more sense using water column ferts since growth RATE= supply, and the substrate will run out fairly quickly.

This method is popular with folks that still believe and cling to the mythical notion that excess nutrients cause algae in a well planted tank.
There is nothing wrong with adding the nutrients in there though. ...But it's not to get around algae in anyway as some seem to think every so often.
At high growth rates that are associated with CO2 enrichement, it is wise to dose regularly before a problem starts since the growth RATES are so high.

Due to this fast RATE of growth, plants run out of something very fast, then they stop/slow down growth, then you get algae.
Add higher light, then it makes this even more critical. Much like oral hygine, do you wait till you have a cavity or do you brush your teeth daily? Maintenace of the nutrients is very similar. I've reasoned out a decent method to estimate the nutrients so you don't need a test kit even, Chuck's calculator helps the Chemically challenged.

But it still takes work to keep up with that type of system/method.

Non CO2 tanks can handle much more abuse and different fert routines since the RATE of growth is so slow, the lighting is less. Both of these make it possible to balance fairly well the fish waste production with the plant's growth RATE with no algae issues.Algae growth is slower(limited with CO2 and light), therefore herbivores can harass algae at a faster rate per critter adding less NH4. NH4 ratio uptake is very high in a non CO2 tank vs a CO2 enriched tank requiring less energy to Nitrogen uptake/assimilation into Amino Acids.

You can obtain a robust growth rate, not as fast as a high light tank, but a nice rate of growth and very healthy growth using low light and CO2.
This gives the grower a nice middle ground so that they can get away with less water changes(if that is their goal), more wiggle room with dosing, more reliance on a substrate fert routine(if that is their goal), less light= less algae, less CO2 demand=> more CO2 wiggle room, more % of nutrients from fish, easier pruning schedule(less growth rate), less electricity and lighting cost.

This tank type bridges the gap for those folks that kick and scream about water changes, forget to dose, like substrate dosing, don't want so much work etc, but still have the nice plants associated with CO2.

Each method has it's trade offs though, there is no perfect method/system but the low light CO2 enriched tank does come close to that goal.

All the plants essentially do fine at 2w/gal of NO FL's, add a reflector to that and that makes a nice easy to grow tank+ CO2.

So you have:

Fast growth, high light + CO2, more water column dosing
Medium growth, low light+CO2, a number of dosing routines
Low growth, non CO2, slow growth, number of routines but the easiest is to let the fish add the ferts with an ocassional top of of tap water, GH/K+ etc.

You can dose the water column(you do actually anyway) in a non CO2 tank without algae also and not add much to the substrate(no soil etc).
This works because fish food is the the dosing part. The waste supply the nutrients and these come in to the water column, not the soil and this becomes the main source of most nutrients as the tank becomes older.

You can dose inorganic ferts though and get good results also, but there's little reason to by having a good fish load and feeding the fish.

All 3 tank types can look very good. Yes, there are grades in between, but these are general tank types.

You can get away with more water column or substrate dosing for each routine to some degree. This gives folks 3 easy methods to suit most folk's routines and taste.

Tom Barr
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