# Thinkness of media affecting biological filtration



## chiroken (Sep 25, 2007)

Always reading and learning.....

Planning on a 6' sump under my 8' 300g tank. Thinking of using foam as biological media, many seem to say poret foam is the best. You can get foam in 4" thicknesses. I also regularly read that bb on grow on the first 1 1/2-2" of foam depth and I don't understand why this is. Water is passing through the entire foam. If the reason is lack of oxygen, why then do some stack foam layers with just a small space between each piece of foam? I can't imagine the water is re-oxygenating in a 2" space of water. If the reason is lack of nutrients then the same response...some stack layers.

The sump was previously for a reef tank with baffles. In the vertical baffles were pieces of 2" thick matala mat. If water flows up or down a baffle that is 10-12" high then are bb growing only on the first 2" of the matting and the rest is just mechanical?

This is a key question as my goal is to maximize biological filtration after initially doing mechanical filtration. IF the baffles do very little bio filtering then I need to remove the baffles and re-design the sump lay-out.


----------



## chiroken (Sep 25, 2007)

Anybody have any insight into this? Or maybe you can refer me to somewhere that would be able to address this?

Thanks


----------



## SupeDM (Jan 26, 2009)

If lack of oxygen was the issue then you would develope anerobic areas in the foam. I would think that depending on flow nutrients may be used up in the upper layers of the foam. Increasing flow would increase the nutrients available. For the second question any where that the water is exposed to atmosphere there will be some gas exchange. What Iwould imagine the spaces between layers is designed to do is allow some oxygen to be absorbed thereby preventing anaerobic conditions.


----------



## Deeda (Oct 12, 2012)

I was looking for the specific info regarding the ideal foam thickness for beneficial bacteria but I can't remember where I found that information. It was either on Dr. Tim Hovanec's site or on the Olaf Deters site that explained the theory & mechanics behind using HMF style filters.

I will tell you that the 2" thick Poret sponge filters are extremely heavy when water filled so I can only imagine how heavy the 4" thick ones would be. Have you looked at the Swisstropicals website that suggests how to use the Poret in a sump or wet/dry filter? I'm pretty sure he had an excellent diagram on how to lay it out.


----------



## BillD (May 17, 2005)

In general terms, the thickness of the foam will have a bearing. With Hamburg/mattenfilters, going beyond a certain thickness doesn't improve the filtration. As well, the pore size will have a bearing, as the various pore sizes will give you different total surface area for a given volume.
In the case of a sump, the ideal scenario would be to prefilter the water prior to the poret foam, so it never clogged. This could be done with polyester matting of the type used for quilt batting or air filtration. This material would be tossed when it was dirty.


----------



## chiroken (Sep 25, 2007)

Deeda said:


> I was looking for the specific info regarding the ideal foam thickness for beneficial bacteria but I can't remember where I found that information. It was either on Dr. Tim Hovanec's site or on the Olaf Deters site that explained the theory & mechanics behind using HMF style filters.
> 
> I will tell you that the 2" thick Poret sponge filters are extremely heavy when water filled so I can only imagine how heavy the 4" thick ones would be. Have you looked at the Swisstropicals website that suggests how to use the Poret in a sump or wet/dry filter? I'm pretty sure he had an excellent diagram on how to lay it out.


I've been to their site before and they have diagrams of sump set ups. In 1 they use vertical pieces with water between each piece(no thickness given). In the other they put a spray bar over stacked horizontal foam (mostly wet) of 2", 4", 4" thickness with no water between each sheet. That's 10 solid inches of foam. So again I wonder which is actually accurate as to foam thickness and bb growth. The 2 designs seem to contradict each other if thickness makes a difference.



BillD said:


> In general terms, the thickness of the foam will have a bearing. With Hamburg/mattenfilters, going beyond a certain thickness doesn't improve the filtration. As well, the pore size will have a bearing, as the various pore sizes will give you different total surface area for a given volume.
> In the case of a sump, the ideal scenario would be to prefilter the water prior to the poret foam, so it never clogged. This could be done with polyester matting of the type used for quilt batting or air filtration. This material would be tossed when it was dirty.


I would like to actually find some documentation as to why filtration doesn't improve with thickness, it doesn't make sense to me. I do understand pore size affects surface area and swiss tropicals gives the amount for their various foams.

For pre-filter, I am 100% thinking of doing this with something like filter floss sheets or something. I haven't been able to figure out how. I was going to go wet/dry with a DIY storage shelf system so the top shelf was floss. I am planning on building the plumbing as the silent bean animal system so the pipes that enter the sump need to be submerged. Haven't figured out how to submerge the ends and work a prefilter. Easy sump design is vertical poret foam between inlet and outlet of the sump. Any ideas?


----------



## tankhead (Aug 8, 2008)

I think as long as water is passing thru the filter then bacteria will grow. Bacteria aren't going to be so efficient that they remove all the nutrients and O2 thru each and every pass. I do think there is a point of diminishing returns where you can get to overkill. Having said that, it is better to be safe than sorry and if the system can hold the media you should use it. Also keep in mind that a benefit of having the sump is that you've basically increased the volume of water that your fish can use, hold waste, etc, so your 300g tank is now 300+.


----------



## CrypticLifeStyle (Dec 14, 2009)

http://www.janrigter.nl/mattenfilter/ maybe this can help


----------



## chiroken (Sep 25, 2007)

CrypticLifeStyle said:


> http://www.janrigter.nl/mattenfilter/ maybe this can help


So this artice completely contradicts many other website. If understood correctly, it is saying for proper bio filtration through foam turnover is no more than 2x tank volume per hour and that "stacking" foam pieces in series is useless. Only 1 foam and with that, colonization is basically only in the initial part of the foam and the rest of the thickness is just for structural support to hold the foam in place.

Even more confused now. I was hoping for the 1st foam to function as mech. filtration to be periodically rinsed with the foam pieces downstream to be biofiltration as they shouldn't really get clogged with muck.


----------



## Deeda (Oct 12, 2012)

The article that Cryptic linked to is really dealing with the HMF style filter which is normally used vertically as the sole media in a tank. The 2x turnover rate was linked to the speed of the water moving through the filter foam without dislodging the beneficial bacteria (BB) from the media pores but yet still enough flow to bring nutrients for the BB. I didn't re-read the article so I don't remember what science or literature was cited to provide the math that determines ideal flow through the foam media.

I'm fairly sure that much of the information for determining proper biological and mechanical filtration is derived from either sewage treatment plants or aquaculture systems for large fish farms. This science is more than I can understand but I don't know that it is really necessary to understand for our aquarium filter needs.

I know you mentioned possibly using the DIY storage drawer bins method for the initial flow from the aquarium. Floss or polyester batting would catch the most debris at the top drawer and you could do additional layers in the 2nd drawer. You could also use progressively finer Poret foam laid flat in the other drawers. Depending on the size of the sump, vertically placed Poret would also provide added filter capability and would be easy enough to remove individually for cleaning.


----------



## CrypticLifeStyle (Dec 14, 2009)

Have a picture of the sump you can post? There's all sorts of factors that will determine how thick you want it, and how it's used isn't a issue vertically or horizontally not that you mentioned either from what i read, and the math is sound from my readings, and all aquarium based, not municipal. All the matten filter sites that explain the math are all pretty much based on the same equations. Curious if the foam used in the sump when it was a reef were just bubble traps, and mechanical filters. I havn't run across any reef setups using foam for biological really.


----------

