Soil substrate again

[GRGeorge]

I'm watching for some time this forum (have read a lot) and since I believe it has a very good level in this field (with contrasting opinions some times, which I like) I would like to ask for some help.
I feel sorry for the length of my post but I believe it would be understood why it is, if anyone (who has the strength) reads it all.

I have understood that most of the people here use fluorite, onyx, etc. but this is an approach I would like to avoid (availability is limited here) and I don't think also that fluorite is a panacea (so other alternatives should exist).

I decided to go to the soil solution looking for various types (available here). Most of them are not quaranteed for the ingredients and there is lack of information generally.
I finally set-up a tank using humus substrate which is "decomposed frozen through black sphagnum peat'' with added fertlizer (~1% of N2, 0,8% of P and 0,8% in K).

For using it I made the following procedure :
1) I put 1'' of humus at the bottom and 3'' of water and I disturbed it a lot. Then I emptied the water. The thought was to remove excess fertilizers and humic acids.
2) Then I put 1.5'' of fine gravel (rather thin).
3) Fishless cycling for a couple of weeks, emptied ~95% of water and planted medium-heavy but mainly with stem plants (crypts are the only typically root feeders).

The tank (25 gal) is very lightly stocked, mainly I make top-off and only every month I make a 30% water change. There is a diy CO2 (but I don't replace it regularly). No fertilizers added. Only 1.4 w/gal lights.

I didn't experience any diatoms at the beginning and and only for a couple of months I had controlable amounts of green algae (green according to DUPLA definitions).

All the plants from the very start were/are going strong. Even species that I'm struggle with in my main display (Alternathera, mayaca etc) are doing excellent and the red color of macrandra,altern. is very deep with only this light and maintenance.

Now 6 months from the beginning the algae is minimum and I'm very pleased with the result (and the fish also spawning there). The water remains alkaline and medium hard. The roots of stem plants are long, healthy and very binded with the humus.

Because of these results, I want to make the same change in my main tank. But before I proceed I have some critical points which should be clarified but I think only according to experience and not by reading (IMHO).

The main tank (50 gal) is rather heavily stocked with fishes and heavily with plants (press. CO2, undergravel cables, 3.8w/gal). This tank has cost me a lot (time and money), with medium sized gravel substrate (PMDD,root fertilization) and is very unstable with chronic algae problems.

The aim is to have a long-term stable situation with good appearence (ferocious growth is not first priority), in a more natural way, but using also some high-tech elements (fluorite is not an option), mainly for helping plant species considered to be generally difficult.
According to the up to now results and the goal to achieve the 1,000,000 $ questions are:

1) Will this substrate work with these completely different conditions ??? (one point is to lower the light?)

2) Should I put some amount of commercial substrate with the humus? Walstad in her book had metal toxicity (she believes) when mixed soil with laterite, but here we don't have pure soil (does it make a difference?).

3) Using peat only substrate considered no-no due to further decaying organics and to vast amount of nutrients (remember the wash-out? ). But in humus all the decaying process has been done or continues very slowly. With such a high CEC (~200) I think that most of the nutrients will remain in soil (algae can not use them, can they?). So can we use safely such nutrient rich substrate?(which lead us to the next question).

4) According to Tom Barr (and not only) "
Less importance is placed on the nutrients in the substrate when the nutrients are available in the water column " and "
Plants will take it (nutrients) from water column if it is available ". The opossite is true then? (My experience so far shows to this way).

5) A big problem is the compaction and the refreshement (strip down) after 2-3 years BUT for pure soils (according to my knowledge - long term stability achieved by Walstad in light fishstockings). The main thought is to put also the undergravel heating cable, but not to use it till I see a decline to plant growth and certainly after the first year or more, so to avoid the compactness (can be avoided with the small currents and replantings?) and to help (with fertilizers at this point) the humus to refresh macro-nutrients (binding properties remain after this time??).


PS. I'm very sorry (again) for the length of my post but I wanted my plan to be clear in detail, so any (appreciated) answer can focus on the queries.

[plantbrain]

"1) Will this substrate work with these completely different conditions ??? (one point is to lower the light?)"

That's a very very big point.
You treat one tank like a non CO2 tank generally and likely don't keep up with the high light one with CO2.

It's like a car going 40km/hr vs a 120 km/hr. If you crash one, the result is far worse(and you get algae). At 40km/hr it's not so bad.
At 40km/hr you get far better gas kilometerage per liter of gas(nutrients).
The faster you go the faster the the nutrtients are used up.

"2) Should I put some amount of commercial substrate with the humus? Walstad in her book had metal toxicity (she believes) when mixed soil with laterite, but here we don't have pure soil (does it make a difference?)."

You are mixing non CO2 with CO2 methods, DW's method is not the only method using soil. I use peat in all of my substrate and detritus from an established tank. You should be able to find Profile or turface in your area or something similar. That would be fine and so would iron filings.

"3) Using peat only substrate considered no-no due to further decaying organics and to vast amount of nutrients (remember the wash-out? ). But in humus all the decaying process has been done or continues very slowly. With such a high CEC (~200) I think that most of the nutrients will remain in soil (algae can not use them, can they?). So can we use safely such nutrient rich substrate?(which lead us to the next question)."

I've used peat only capped with gravel. It works. I know others that have and it's a good method.

"4) According to Tom Barr (and not only) "
quote:
------------------------------------------------------------------------
Less importance is placed on the nutrients in the substrate when the nutrients are available in the water column
------------------------------------------------------------------------
" and "
quote:
------------------------------------------------------------------------
Plants will take it (nutrients) from water column if it is available
------------------------------------------------------------------------
". The opossite is true then? (My experience so far shows to this way).

Yes, they will go after the nutrients wherever they may be. It's just easier for them to get it from the water column vs the substrate.

Often in nature the water column is poor in nutrients so most studies show much of the nutrition comes from the soil, but when researchers add nutrients to the water column in sufficent amounts, many plants switch over and far less comes from the substrate.

Iron needs to be in the substrate and lots of places for bacteria and also peat.

"5) A big problem is the compaction and the refreshement (strip down) after 2-3 years BUT for pure soils (according to my knowledge - long term stability achieved by Walstad in light fishstockings). "

I suppose. I've had great success using Flourite and DW method in place of the coveted soil method. I use a bit more peat and detritus added to the substrate but that's about it. No soil is added and the result are extremely good for non CO2.

"The main thought is to put also the undergravel heating cable, but not to use it till I see a decline to plant growth and certainly after the first year or more, so to avoid the compactness (can be avoided with the small currents and replantings?) and to help (with fertilizers at this point) the humus to refresh macro-nutrients (binding properties remain after this time??). "

Sell the cables.
No use for a soil tank. You want to keep things down in the substrate, not flowing through. Remember this is a much richer substrate than cables were designed for.

I'd try and find some profile/turface. Then add some to the bottom layer along with ground peat and the detritus from the old tank(keep only the dirty mulm left on the bottom of a bucket after a water change with a a gravel vacuum).

For a non CO2 tank, you'd add more organic material(mor epeat and detritus).

But if you are going to slow a tank down, use the lighting and decrease the amount say down to 2w/gal if things run too fast for your routine.

Chopsticks are useful for loosing up any compaction issues. Do a section after each pruning/water change, say 1/4 to 1/2 the tank once every few months.

No issues.

Regards,
Tom Barr

[GRGeorge]

Thank you for the reply Tom, but some points still need explanation (plus some more :) ).


1) Does the CEC in soils(humus) declines with the time?

2) Since you mentioned about the research (soil vs. water fertilization), is it known if there were significant differences in growth between the two methods (considering of course the other variables the same e.g. lighting). IME there isn't much difference in most stem plants.

3) Another point you refered, is to cut the amount of lights to avoid big growth, but I think in rich nutrient substrates the plants must grow fast to overcome other problems (e.g. roots rotting or even algae). So is it wise to cut the lights in such substrates?

[plantbrain]

1)
I think if you could isolate just the CEC of the gravel itself, yes, each space becomes occupied.

But the biology becomes very active and contributes to this system and the end result is higher CEC with time.

Old established tanks do better than new ones. Adding the organic matter, the detritus from an established tank instantly adds all that bacteria and critters to the gravel.

Most tanks do better with time. The bacteria, fuguns and detrivores process and demineralize waste very well in older tanks. They are much better at exchange and processing chemicals/waste/plant nutrients than static gravel.

But they need good stable conditions and time to get established well for the waste/fish/critter load coming in to the tank.

2)

I see better growth with water column vs only substrate fertilization.
This is easy to compare also. Using RFUG filter insures nothing is in the gravel except biofilms on the grains and not much else.

But perhaps the take home message for substrates, slight enrichment with peat/detritus/mulm/laterite or Flourite etc is okay and will only add to the water column dosing routine. Relying on the substrate only is something for Non carbon enriched methods. CO2, Excel etc will drive the plant's metabolism too fast to keep up with roots alone generally. A few plant might do okay/well.

You cannot test the nutrient easily in the substrate either. Do you have enough of NO3 or PO4? You don;t know with the substrate and you also cannot measure the uptake rates etc. Riccia/attached/floating plants will not get much from substrates.

Studies I've read indicate that the plant will switch from root feeding(when the water is lean as is most often the case with a number of nutrients) to water column feeding when there are nutrients present in the water column that they can take up foliarly through their leaves.
Seems it's just easier to transport the nutrient where it's need than having to actively pump the nutrients from the roots.

3)
Plant health is pretty good at low light but you can go so low it's tough for the plant to grow leaves or roots. Most plants allocate root growth first then the leaves given a choice or either/or.

But plants only have so much light and this becomes the limiting factor(as it really should be). Does not matter if add 2x the nutrients, at some point the plants need more light, not nutrients to grow faster.

I've never been a big fan of rich substrate, Flourite + peat and mulm is about all I'll use. I'll add a bit more peat or mulm if I want it richer for a non CO2/Excel tank.

I see no need to do that for a CO2 plant tank. A little is fine till the tank settles in.
For the non CO2/non Excel tank you really don't need much nutrients(this is generally all from the fish feedings) since the tank is limited by CO2 and some plants may be limited by other nutrients.

But if there are the same amount of plant biomass, and you have 1/2 the light(say 3w down to 1.5w) and the same herbivores, the algae are going to grow slower if all all. The plants are still shading it, the herbivores are attacking it at the same rate etc.

I had 2 x 28w over a 60 gal cube with CO2, KNO3 etc. It grew pearl grass and pennywort, crypts great. That's less than a 1w/gal.

Regards,
Tom Barr