# Unusual application - Perlite as a filter medium



## scoach1999 (Mar 20, 2004)

Very cool, PlantView.

Thanks for sharing. Oddly, I had just purchased some Perlite yesterday at HD to use in my aquarium. Hmmm...

Earnest Steve


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## DennisRB (Apr 13, 2004)

Is this stuff ever used as substrate? I think using it as a filter is a good idea.


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## cich (Aug 5, 2003)

Not sure if it would ever stay at the bottom... or would it eventualy get waterlogged enough?


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## scoach1999 (Mar 20, 2004)

Perlite is actually rock with millions of tiny bubbles in it caused by super-heating, kinda like how popcorn does when it pops.

There is little point using it as part of yuor substrate layers. There are already so many products available that are superior in many respects (one of the very best being Eco-Complete). Perlite has no iron and is not fortified with any micro or macro nutrients. It is kinda of a "filler" that can absorb moisture (and nutrients when you fertilize) and will slowly disperce moisture as soil begins to dry. 

As a water-polishing filter medium it should work great, especially when those little bacteria colonize it.

I'm trying Perlite out in a DIY CO2 reactor to create more turbulence in the chamber as the H2O and CO2 pass out the bottom into the tank (hmmm... Maybe do a little water polishing in the process!).

Just my 2 cents.

Earnest Steve


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## compulsion (Mar 2, 2004)

man i had this very same idea today, im sending my mum up B&Q tomorow to pic me up a bag to mix with my and.. and they say its pourous so i figured i could fill my bed filter with it, im sure it would provide more area for bact than the standard sand i have at the mo...

just read above posts... yeah it can be used as a sub and lots of people use it mixed with eco-complete like scoach said. but scoach some people use ONLY flourite... for some reason


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## scoach1999 (Mar 20, 2004)

Flourite is porous and the clay it is made from has a lot of iron in it, so you don't need to dose Fe Iron at all. It will absorb some nutrients from the water and so will gain some nutrient substance, but by itself it simply doesn't compare to the rich biological and nutrient root food that Eco-Complete offers your plants.

Check out each product's details at thier respective websites and see for yourself!

Eco-Complete is from CaribSea and Flourite is a Seachem product.

Earnest Steve


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## compulsion (Mar 2, 2004)

? flourite isnt just made by seachem... flourite is used for lots of things other than planted tanks. and it has NO Fe in it. its inert.


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## scoach1999 (Mar 20, 2004)

::heavy sigh::



> Flourite is a natural porous clay substrate that is naturally rich in iron. The good news is that using Flourite (according to Seachem Research Director, Gregory Morin, Ph.D.) you don't need to use Fe iron dosing drops and your plants will have the iron they need at their roots.


Hey, the guy is a Ph.D. 

Who am I to argue with him? But... You can if you want to!

A little homework goes a long way, yes?

BTW... I know what flourite is. And in particular I was referring to the product by Seachem that is called Flourite.

Earnest Steve


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## dogg76 (Jan 31, 2004)

if you used perlite in a filter, would it absorb nutrients out of the water so the plants couldnt use them? has anyone else tried this? i would like to hear some more opinions on this...


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## scoach1999 (Mar 20, 2004)

Hi dogg76.

There are a great many porous filter mediums available commercially today. To the degree that they are porous and do have a absorptive quality predisposes them to aborb water and anything that happens to be in the water that is small enough to be absorbed. Logically speaking, nutrient would be absorbed, but only until the absorption reached a stasis level, i.e., the absorbing is not infinite and will not continue forever. The perlite would tend to absorb somewhat for a short time and level off when it reached a saturation point.

Would perlite leech out the nutrient and leave the water reduced? Not likely. The reason it would not leech out nutrient is that it is not nutrient-selective. It would absorb the water right along with the nutrient, so the amount of nutrient and water absorbed would be in about the same ratio as the water and nutrient remaining in the water column.

While perlite is porous, it does not have the kind of retention capability of, say, the co-polymers on the market that are used in soil gardening for retaining and dispersing H2O in the soil. These co-polymers have an enourmous absorbing capacity -- something in the range of 500 times their dry weight. They are very useful in their intended roles.

Perlite, on the other hand, doesn't get any larger when you soak it (not so you'd notice). The physical structure of perlite is much more rigid. The only absorbing is what can get into the surface. In other words, perlite does not really expand -- it is just porous. The structure of it is not as resilient in water as the afore-mentioned co-polymers.

The fact that perlite does absorb at all (because it is porous) made it good for use in garden and potting soils where water retention and release was desireable. With the advent of the co-polymers, using perlite for this purpose is edging toward obsolete as the co-polymers are cheap and work so incredibly much better in the soil.

As a filter medium, perlite is stable and inert. It should be expected to host nitrifying bacteria on its surface and possible in the pores of the grains.

Now, if you are familiar with the idea of a mixed-field nitrification/de-nitrification bacteria bed, perlite might very well be a good medium to facilitate this kind of culture.

You are probably familiar with the notrogen cycle and with nitrifying bacteria. A lot of people are aware of the build up of nitrates in the water as a by-product of the nitrogen cycle that results from the aerobic nitrosomonas and nitrobacter bacteria. However, a lot of people are not as readily aware of the anearobic bacteria that feast on nitrates and convert it into harmless nitrogen gas that escapes into the atmosphere through the surface of the water column (along with O2 and CO2).

Once that beneficial anearobic bacteria is established and stable it may go a long way toward helping to control nitrate levels in the water column. Research studies have indicated that in the right types of media, aerobic and anaerobic bacteria can survive together in communal harmony effectively producing nitrification and de-nitrification at the same time. It is believed by some that this beneficial anaerobic process can occur deeper inside a porous medium's surface where the tiny bacteria cna live, but where O2 is not as available as it is on the surface of the medium grains. Seems to make sense.

Some of this research is fairly current and can be found on the 'net under topics of anaerobic bacteria and de-nitrification (particularly related to the biological purification of drinking water).

Also, refer to PlantView's post of Tue Mar 23, 2004, 1:00 am (see above), with the "Schundler" link about using perlite in practice as a filter medium.

In any case, using perlite is safe enough.

Hope that helps answer your question.

Until later,

Earnest Steve


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