# Is this pool filter media OK for a substrate cap?



## Moose-Factory (Feb 13, 2008)

Hello, I'm writing because I've just acquired a bag of pool filter media that I might like to use as a cap over the soil layer in my aquarium.

My hesitation is that the granules are around only a half an mm in thickness. They are all the same thickness. I'm concerned that 1/2 an mm may be too small a granule size, as Diana recommended 2-4mm in her book, but didn't really elaborate much on why that size.

Here's what I got: http://www.amazon.com/gp/product/B00JJ5GXSK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Should I stick with this or opt for something thicker. Does granule size matter? How does granule size effect the aquarium?

Thanks!!


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## Yo-han (Oct 15, 2010)

Never used El Natural, but I can tell you that using sand with a rich substrate below is risky. The risk is that too little water movement is through the substrate which leads to anaerobic spots. Pool filter sand is better compared to regular sand because the more rounded grains are less likely to compact. Still I myself would never use a rich substrate below sand.


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## GadgetGirl (Sep 25, 2013)

Pool sand is fine. As for the rich media, if you properly prepare it by rinsing, draining and mineralizing, you won't have any problems. I use Flourite Black sand (super fine) over topsoil with zero issues. I have also used play sand over Miracle Grow Organic Choice with no problems. Your total substrate depth should never be over 2 in. 

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## Michael (Jul 20, 2010)

"Go not to the elves for advice for they will say both yes and no." --JRR Tolkien

Both replies are right. When using a fine sand with a soil substrate, be sure the soil is well prepared, and both sand and soil should be in thin layers, certainly not more than 1" for each and less if you can get away with it. Thin layers can work well in small tanks with small plants, but may be hard to plant in if the tank and the plants are larger.

Fine sand really benefits from Malayan trumpet snails. Their gentle burrowing helps to prevent the anaerobic conditions from developing.


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## Yo-han (Oct 15, 2010)

+1 on the MTS!


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## Moose-Factory (Feb 13, 2008)

GadgetGirl said:


> Pool sand is fine. As for the rich media, if you properly prepare it by rinsing, draining and mineralizing, you won't have any problems. I use Flourite Black sand (super fine) over topsoil with zero issues. I have also used play sand over Miracle Grow Organic Choice with no problems. Your total substrate depth should never be over 2 in.
> 
> Sent from my Nexus 5 using Tapatalk


Thanks for the replies. I'm still a little wary of using granules this small.

If I did decide to use something larger, you mention fluorite. My understanding is that fluorite granules are a smaller than gravel but larger than sand, which would probably allow for greater aeration potential than sand. Would regular or red flourite be suitable as a casing layer in a "natural" aquarium? (black flourite may be too dark in color for my taste).

If I do decide to use flourite, I've heard that it is "rich in ferric iron" and other trace minerals. I'll already be using the soil layer below it to provide fertilization and trace minerals, so would using flourite overload or toxify my aquarium with iron or other stuff?

Diana mentioned in her book the risks of having too much iron in a tank using the "natural" method. Should I be concerned with fluorite then?


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## TropTrea (Jan 10, 2014)

I will have to disagree with several points others brought out.

1. I always try to use a finer substrate on my planted tanks then I do for my other tanks. My ideal is the what is sold locally as fine red flint pool filter gravel. It usualy is available in four grades fine, medium, coarse, and extra coarse. The Coarse works good in Cichlid tanks. without plants. I like the red flint for its darker brown to reddish brown color and if mixes beautifully with black diamond gravel for a dark substrate look.

2. While most of my planted tanks have been 30 gallon plus I prefer to keep the substrate in the 3" to 4" range. So far this worked out beautiful for me. What I usually do is start out with a layer of laterlite equal to a half box, then add the substrate gravel just enough to cover it at least 1/4" all around. I will repeatedly layer it like this untill I get to the last layer of gravel which will be 1" thick. 

In the past I have had tanks running with this combination for over 5 years with no problems.


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## Michael (Jul 20, 2010)

TropTrea, the difference here is that Moose-Factory is using a soil layer. Your gravel and laterite substrate is not nearly as prone to develop anaerobic conditions because there is little or no organic matter actively decomposing in the substrate.


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## TropTrea (Jan 10, 2014)

Michael said:


> TropTrea, the difference here is that Moose-Factory is using a soil layer. Your gravel and laterite substrate is not nearly as prone to develop anaerobic conditions because there is little or no organic matter actively decomposing in the substrate.


Initially I would have to agree with you. However over time the waste material of the fish does get into the gravel and does start to decompose. When I do water changes I might siphon off the water from the bottom but I'm very careful to not upset the gravel. This causes the fish waste to accumulate to some extent and over a period of time creates a considerable amount of organic decomposition.

I'm not big on fertilizing after the tank is initially seasoned and cycled. If anything I'm adding iron especially during the early days of establishing the tank.


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## Michael (Jul 20, 2010)

You are correct that over time there is an accumulation of organic matter in an inert substrate, and eventually this mimics some effects of a soil substrate. But it happens very gradually, and the organic matter is in much lower percentage than found in most potting soils commonly used in aquaria. Also, the mulm that builds up in an old tank is already highly diluted, broken down, and "rinsed" so that it does not have the fresh organic matter and excess nutrients that many soils do if not properly prepared.


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## BruceF (Aug 5, 2011)

I've cleaned out a few tanks in which the substrate smelled horrible upon the disturbance but I can't say I have ever actually understood what the problem is with anaerobic conditions in a substrate. Can someone explain what the actual problem is?


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## GadgetGirl (Sep 25, 2013)

I can't explain this, but I will say when I broke down my dirt substrate tank after it had been running for a little over a year, the substrate just smelled, well, earthy. No bad smells and certainly no evidence of anaerobic conditions. The fish were fed well and I never came even close to vacuuming the substrate. 


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## Michael (Jul 20, 2010)

BruceF said:


> I've cleaned out a few tanks in which the substrate smelled horrible upon the disturbance but I can't say I have ever actually understood what the problem is with anaerobic conditions in a substrate. Can someone explain what the actual problem is?


Almost all substrates have small areas of anaerobic condition. This is normal and part of the nutrient cycle of the tank. But when there is a large amount of organic matter and little oxygen penetration into the substrate, the beneficial aerobic bacteria use up all the oxygen and die off. Then anaerobic bacteria take over the decomposition of the organic matter. These bacteria live only in oxygen depleted environments, and instead of using oxygen and releasing CO2 during respiration, they produce hydrogen sulfide (H2S) instead. H2S is toxic to plants and animals, and has the characteristic smell of rotten eggs.

The first bad effect is to kill plant roots if the plants cannot move enough oxygen from their leaves to the roots to counteract the anaerobic conditions. If the H2S is released into the water, it can kill all the fish, plants, and invertebrates. Very bad indeed!

There is a complex system of aerobic and anaerobic microenvironments in healthy substrate, and this is controlled by many chemical and biological processes. When we set up a soil substrate tank, we do a number of things to help maintain this balance and prevent development of large anaerobic areas. The cap particle size is just one of these techniques.


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