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Substrate solution/water column interaction

4910 Views 5 Replies 3 Participants Last post by  plantbrain
If you have a proper substrate layer, you will din that the substrate solution will have different characteristics than the water column. This is valuable as it makes certain nutrients soluble in the substrate solution but not in the water column. Additionally, nutrients would be held in exchange sites on the substrate particles where plant roots can get to them but not algae.

I high exchange rate with the water column should be detrimental to this as it would bring O2 and impact the solubility of nutrients. In addition, a higher leaching rate would occur potentially leading to higher than normal levels in the water column.

If the above is true, what makes up a good substrate so that there is some interaction but not too much?
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I have a hard time understanding why folks would want to confine nutrients to the substrate in high light tanks. How exactly does that prevent algal growth or is there some other motive?

Under what condition(s) and for what application(s) would substrate layering be appropriate? For example, this method doesn't present well to folks who terrace or trim/replant frequently.
The only advantage is the lower redox values making something(nutrients) more available. This can occur in the microsites on a porous grain of substrate without disturbing the bacteria.
Even if the gravel is moved around, the grain still stays the same.

The roots produce O2 around the active growing region.

Placing nutrients into the gravel vs the water column is not going to raise the O2 levels, it would lower them. Growth would be slower/similar, not slower.

Growth, or primary production is sometimes measured via O2 production/evolution. So if growth is slower, then there will be less O2.

There's some of the water column and some of the substrate nutrient sources going on in every nice rooted plant tank.

You need both, iron is very particular to have in both locations.

You can use macro's in the substrate but this has been going on for decades with soil(pre soak it for 3-4 weeks to remove the NH4), other things like osomocoat etc. Changing to non NH4 urea based products may help the initial set up, but the long term growth still demands a source of nutrients, you will need to resupply nutrients and wait till the roots grow over to where they are placed.

There is no such wait nor internal transport needed for the water column.

But if you think about like this, this may resolve any differences you and others might have about this issue:

__Let the plants decide__, provide both locations for the macro's/micro(without any NH4 except from fish), crank the hell out the CO2 provide even moderate light and do your water changes, pruning etc.

Fish waste is enough to grow most algae.
How do you plan to put that into the gravel?

If you really want to look into this dynamic, I have some papers to consider reading and also some methods you might want to start with first, RFUG and plain old sand makes a nice baseline to compare with since it does grow plants well when dosing the water column.

From there, you can add different things to the substrate(macro's NH4, jobes, iron only), flow rates(fast, medium, slow, very slow, none) etc.

Tom Barr

Tom Barr
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Tom, I would like to read up on those papers. Please PM me or post them here. Thank you.

I have heard of and understand the logic of macros in the substrate in lower light tanks and using root tabs for heavy feeders under low/high light. What I really don't understand is why some folks, whose opinions I highly value, insist that macros in the substrate is crucial when dealing with high light setups. Is the benefit of the lower redox values lead to such significant difference(s) as to warrant its use?

If macros are so important in the substrate, then is there some product or DIY procedures that make macros safe and conducive for the application in question?

Sorry if I have strayed from the original topic Art. :oops:

Welcome to APC!

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Email me off list, I am not allowed to post papers unless you can google search them etc, I use a university journal serach but all things aquatic plant are listed at IFAS here at UF. It's just bibiolography, but you can search for the pdf's and libraries and see if you can get some copies.

Tom Madsen, Nina Cedergreen Freshwater Biology(2002) 47, 283-291 is one of the better papers.

But you need to realize a few things first off here.
The ratio of macro nutrients in the substrate vs the water column methods is not that great. Plants STILL get macro nutrients from the water column no matter what type of method you use.

This comes in the form of K+, fish waste in the form of PO4, NH4/NO3 so while some want to polarize the sources, there is still and always will be a large dependace on the water column. O2 and CO2, K+, NH4, Ca/Mg, NO3, Traces are STILL doses in various amounts to the water column.

Now you can try this out your self.
Try to add all the needed macro to the water column.

Next try to add macro's to the substrate in this SAME tank.
Add some under one similar plant and not under another.
Say a jobes stick.

But keep the water column well supplied during the test run.
I and several others found no differences in terms of growth/health.

And why should we? The plant has access to the nutrients and does not have to transport them internally.

Now if you remove the KNO3/KH2PO4 dosing from the water column, and add this to the substrate along with traces, the plants will still grow well, as lopng as this substrate supply is maintained and the water column also has it's dosing routine(Traces/K+, fish food, CO2 etc)

You are only talking about Nitrogen really in this case as plants can handle PO4 stress pretty good, often fish food alone can supply relative decent amounts along with NH4. K+ will dissolve and is added to the water column anyway.

I do recall these tanks need broken down every 2-3 years to resupply the nutrients.

The thing about these tanks I know are not better is the growth cannot be faster/better than water column dosing, there is not transport cost occuring in the plant, the levels of nutrients can be maintained better in the water column and also can be tested much easier.
The water column dosing also maximizes the available light.
You get the simlar results with 1/2 the light using the water column dosing.

Many of you did not have planted tanks in the 1980's and before.
Dupla and other methods at the time suggested this method of putting rich subs to combat algae in the water column.
Much of the research said that plants get their nutrients from the substrate, but the research did NOT say that this produced the best growth, few studies enriched the water column with an already rich substrate.

So this method is actually nothing new, but rather, quite old and tested.
What is new, NH4 causes algae, so adding just NO3 to this method in the substrate to combat algae is a key part.

The other larger issue:
The human variable, I can force any method to grow a nice plant tank if I work at it and that's all I have and have found to work.

I used RFUG's with no nutrients at all in the substrates except bacterial cycling films and did better than my cohorts that did substrate only type dosing.

So was RFUG better than their methods?
If you accept the premise that good aquascapes make a method better, I suppose my method would have been better and the plant health/growth was better also.

But the tap water had PO4 and I did large water changes so.......
Perhaps some folks have PO4, NO3 in their taps and doing 50% weekly water changes sure changes things if you stop adding NO3 to the water column don't cha think?

Many European tap waters have 40ppm of NO3 in them and also high PO4's.

This method along with large water changes works well.
They don't need over 20ppm of NO3 after all................

My point here is that this method is nothing new, nothing I have not tried enough to know what is goiing on. I have a non CO2 tank that look as good, so is that method better? Or is it the person using the method?

I think it is very clear that PO4/NO3 levels in the water column don't cuase algae issues, so I see little to be gained through this method and it's also very difficult to suggest to folks to rip their substrate all up and replace it with Fertiplant or some ceramic based macro rich clay, when they can just add 2x a week 1/4 teaspoon of KNO3. KNO3 is lots cheaper, easier to test, to reset and does not require any special substrate.
You can modify it easily to suit the tap water, fish load etc aslo.

Your routine, experience, what you have read and knowledge play a key role in which method you chose, but to me, most methods are very similar.

I've done many darling methods of the month/the year etc I thought were the cat's meow at the time.....after trying so many, you begin to see patterns and which are really significant.

Tom Barr
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