Plant specific substrate vs inert. Advantages?


Junior Poster
Sep 18, 2007
Tampa Bay, Fl area
Was just reading an old thread on APC on whether there was an advantage to using a plant specific substrate vs not using. Some opinions seemed to be that in the long run it really might not make much of a difference as long as one fertilized the water column. If someone has a tank with a high fish bioload with an inert substrate that would accumulate a good bit of mulm and a fairly lightly planted tank, would it really affect plant growth/health if the water column was not fertilized heavily/regularly? I'm interested in the answer as this will help me decide which way to go with my substrate.


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
Light is what drives plant and algae growth. If you have high light intensity the plants will be driven to grow as fast as the nutrients allow them to grow, and those nutrients can be in the substrate or in the water column or both. So, whatever you use as a substrate, you need to provide the amount of nutrients the plants need to grow at the pace the light dictates. One advantage of having a substrate with nutrients in it is that you don't have to be as rigid about always fertilizing the water every single day your fertillizing schedule dictates.

You don't have to buy a commercial substrate that contains nutrients to have a nutrient rich substrate. You can provide the nutrients by using substrate fertilizing, or by just making your own nutrient rich layered substrate. The latter is how the Walstad method is done - using soil as a substrate layer, to provide nutrients.


Junior Poster
Sep 20, 2005
I haven't used inert gravel or sand in a long time, so I'll briefly mention my experiences between fluorite and ADA aqausoil.
Most people would likely agree that ADA provides a much richer substrate compared to fluorite, so one would not necessarily need to be as tentative with dosing the water column as you would expect.
I decided to put this to test after using fluorite in a smaller (20g) tank for well over a year. I had good growth, although it was also high light and I had to inject Co2 like crazy and if I missed a couple days of dosing or dosed too much, algae would start taking over in a hurry. If I kept on schedule, it looked great and algae was quite minimal.
Then I went with a larger tank (90g) and decided to try ADA. The thing about ADA is that it's so jam-packed with nutrients that you can get away without (or barely) dosing and have a beautiful tank. A guy in my club doesn't dose his tank and it looks spectacular. I'm not that faithful and decided to dose a little bit, at least.
To be honest, I probably only dose 2-3x a week at the most, but coupled with the water changes every 4-5 days and the aquasoil, the plants don't seem to need anything more. In fact, I've tried dosing every day and algae seems to grow faster, so I back off. The lighting is also somewhat high, but anyway...
As the other person was saying, ADA and probably some of the other plant-specific substrates, allow more room for error in terms of dosing.

This last part is more of a question -- don't some plants (crypts, swords, for example) prefer to take their nutrients from the substrate?
Or will they take "it" however they can get it?



Lifetime Charter Member
Lifetime Member
Jan 23, 2005
Dragomelj, Slovenia (EU)

Here I use only sand, but ofcourse I dose water column.

Tom Barr

Staff member
Jan 23, 2005
I do not think the "preference argument" is valid nor correctly applied when folks suggest it.

Do I want a larger Crypt or sword plant to begin with?
Start with the goals you want there.
Few folks want ominous massive plants.

Adding more will produce faster growth folks often claim.
If you are adding enough water column ferts, these plants should have no issues at all!

The problem is and where folks louse things up: they do not add enough water column ferts and the plants do not look that good.

When they add a fert tab under the plants, which use up a lot of ferts as they get larger, the weeds take off again and color up. No one seems to bother testing and makes these assumptions about them.

Why else might Crypts and Swords, both fast growing plants after the root's which have a lot of structure and therefore resources added unlike say Rotala............make such root systems?

Is it for nutrients?

Why these same plants also prodice massive structures in inert soil also? With good water column ferts?

Consider where these weeds are found.........streams and rivers...........what happens there every year and season?

Flooding and water level changes.

So you have two issues here.
One is the shear force due to friction ripping the plants out of the sediments.
They need strong roots to hang on!
The other issue, what happens when the water level subsides in the dry season and the plants are left high and dry on the banks?

No water column then!
So they need root then!

Aquatic plants are almost all opportunistic, they will get nutrients from where ever they can.

Never forget this.

Aquarist seem to want to believe all sorts of muckery.
I'm not sure why, the research suggest otherwise as do the folks that work with aquatic plants in the field etc. Aquarist do not set up isolation experiments to test their claims with respect to sediments. I've never met one yet.

But they often suggest because they add a tab under their sword or it has big roots, that the plant prefers it. There is not one paper that shown this to be the least bit true.

I think if you step back and consider our habits as aquarists, the plants and their growth rates and biomass as they grow, you get a much better method and clearer picture about what is occurring there.

Why "either or", "one over another"?
Such black and white thinking is bad in life as it is here.

Since we sometimes remember to dose the water and the sediment method also works well (this applies to both non CO2, Excel and CO2 enriched systems BTW, but not most Marine systems), why not use both?

This extends the utility and time for the substrate and depletion rate/time of both sources of nutrients. So you get more out of the water column and more out of the sediment.

I've been saying this for a decade.
Folks still do not see the usefulness here for some reason.

As far as adding ferts to a sediment rich tank and getting algae, how can this be due to the water column ferts when we can add ferts to an inert system and not get algae?

You need to answer that question before you suggest that leaner nutrients in the water column are the causes for your algal issue.

I can add 50ppm of NO3 and 5ppm PO4 and 2 ppm of Fe, even 5-6ppm and not have any algae.

Likewise I can grow plants in sediment only with no nutrients at any sort other than gases like O2/CO2 in the water column.

No algae in either case.
You cannot blame either method for your algal issues.

Good healthy plant growth defines the system, not nutrients.
We have more than method than can integrated together synergistically.

Tom Barr


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Ten feet from me I have two aquariums with topsoil underlayers and one with an inert substrate. All receive about 2.2 WPG. None are dosed with CO2 or Excel.

The water chemistry in each is the same, with ample supplies of nitrates, phosphates, and hardness. The tank with the inert substrate requires more nutrient dosing than the soil-based tanks.

In the soil-based tanks the plants that are supposed to grow to the surface, like hygro and val, do. All of the plants are sending out new stems. branches, or runners. Without biweekly pruning, the tanks would be jungle-like and I wouldn't see much of the fish.

The tank with the inert substrate is a different story. The S. sublatta is are spreading by runners, but not so fast as to require pruning. The other plants are healthy but are not showing much vertical growth. The hygro, for example, is about 4 inches high, after 5 months of growth. (Its sisters in the other tanks have been pruned at least 3 times in that period.)

I have a sword plant in the inert gravel tank that is about 15 years old. At one point it's leaves reached an average length of about 18 inches. I removed it, cut it back almost to its base, put it into another tank, and let it float for several months. I then planted it in the inert gravel tank. After 5 months it is healthy and about 5 inches high.

From my experience, if high light, CO2 injected tanks are "fast grow" and lower light, non CO2 soil-based tanks are "slow grow", then inert substrate, water column-dosed tanks are almost "no grow." That isn't the worst thing, because as Tom has said, it isn't necessary that every plant or fish be grown to its fullest potential. I like that sword plant the way it is.


Tom Barr

Staff member
Jan 23, 2005
Very true, how fast do you want to grow plants?

Some like the faster growth.
Most really do not once they get it and after 1....2......20 years of hacking it back, tend to think otherwise.

Dosing is "easier" no matter how you slice it with macro enriched sediments.
It does not imply as many seem to assume that you have to dose less to the water as a just means if you do not, you can still get away with it as the weeds still have a nutrient source at least.

Likewise, an inert sediment works if dosed to the water column.
You should be able to get good similar growth rates for each method if you are consistent.

However, the easiest method given our bad habits...warrants the water column + sediment sources for nutrients.

Stick with that approach.
That applies well to CO2, Excel and non CO2 methods.
High and low light etc.

Reconciling the methods, namely non CO2, Excel and CO2 is a goal I have and to help folks see the usefulness for each method given the hobbyist goals.
Things still work the same, just the rates are slower/faster different.

Once you have that in mind, then you can see how they are all very similar.
Then the advice is not as different as you might think and the trade offs make keeping the tanks much easier to understand.

Tom Barr