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  1. #1
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    Biofilter setup question

    I found a scrubbie supplier and was wondering if there were any rules of thumb for how many ft2 of biofiltration surface area you'd suggest for raising relatively low intensity fish (probably catfish, perch or bluegill or ....)

    Per a website I found, scrubbies have an area of about 370 ft2/ft3 of material. My tank is about 1500 gallons and if I stock to end up with adult fish at a density of 1/2 lb per cubic foot (or about 1/15 lb per gallon) for a total of about 100 lb of adult fish to harvest, is there any rule of thumb to suggest how much surface area I need?

    I have two ways I can go but sort of prefer the idea of choice 1 below:

    1- I got an old hot tub pump with a high and low speed from my brother. The low speed uses about 300 watts of power and I was thinking it would be nice to just run that pump at about 2000 and wash the flow down over the scrubbies (maybe 4 ft3 of them?). I would make a distributor pan with holes in it to run down on the top of the scrubbies and make the bed of scrubbies 1 foot deep. It would be suspended above the tank and drain down into the tank. I was thinking about putting a box above the biofilter filled with shredded corrugated cardboard and use that as a filter for a slip-stream of the flow (most would go through the biofilter but some would go through the cardboard filter). I was thinking of putting red worms in the cardboard and letting them live off the fish waste and filter the water at the same time.

    2- I also got a blower with the pump which was also from the hot tub. It blows a ridiculous amount of air and makes a huge geyser. It is also loud. Do you think I need the more air than I will get with the system of spraying down over the box of scrubbies? If so, I can set this up like the aquacube and submerge my scrubbie collection, maybe in a nominally 18" diameter piece of plastic drain pipe and blow a bunch of air in from the bottom. The only thing I don't like about this idea is that the blower is loud and may pull more power than the pump (not sure about that because there is no nameplate data on the blower).

    Any thoughts about the pros and cons and if the pump and biofilter would be sufficient for oxygenating the water for 100 lbs of fish. By the way, I know it also matters how much I feed them each day as well.

    Thanks,
    Wes

  2. #2
    Moderator badflash's Avatar
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    Re: Biofilter setup question

    Scrubbies are great, but should not be used alone. Particulates need to be removed first. I use a bead filter on top of my scrubby filter. If you don't the scrubbies will load up and they are tough to clean. Been there.

    Check
    http://www.diyaquaponics.com/forum/s...e-Brew-Filters for my home brew bead filter.

    As to size, you need to figure that out by killing fish, sadly. I would start with about 10 gallons of scrubbies and see how it goes. If you see signs of stress, go bigger, but with your stocking density and the slow metabolism of your fish, it should be fine.
    The best fertilizer is the farmer's shadow

  3. #3
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    Re: Biofilter setup question

    I was doing some more reading trying to see what else I can learn about biofilters and, although this company has a vested interest in suggesting that structured packing is the best biofiltration solution for a simple trickle-type biofilter, I think they make some great arguments.

    I am a chemical engineer by day and know that structured packing is the best packing to fill a distillation column with - it is consistent in terms of the available flow paths, resistant to plugging (definitely much better than gravel or even random dumped packing, and maximizes the liquid/vapor interface in a distillation column to improve the efficiency.

    I was also happy to see that this looks like a fairly inexpensive way to purchase good quality surface area. I think I may aim this way instead of the scrubbies - but tomorrow is another day!

    Here is a link.

    http://www.biofilters.com/cmydocum.html

    Wes

  4. #4
    Members aquaarche's Avatar
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    Re: Biofilter setup question

    are boifilters necessary if you are using rock medium in your growing bed? and is the ratio of gallons of water per fishtank the same per gallon grow bed 2 to 2 or 1 to 1

  5. #5
    Moderator badflash's Avatar
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    Re: Biofilter setup question

    If you are using a grow bed, it serves as the bio filter. You want twice as much grow bed as fish tank. Far less will do biofiltration, but it won't remove the nitrates and phosphates. The plants do that and you need that much space to have enough plants to do the job.

    Stuctured packaging is what my Aquacube is made from. It works well. Be sure you pick a mesh size of at least 1/2" so it can't clog. The down side to that is it reduces the surface area. That is why I use the bead filter over the scrubbies. You can use a fine mesh bio filter like the scrubbies if you filter out the solids first.
    The best fertilizer is the farmer's shadow

  6. #6
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    Re: Biofilter setup question

    Aquaarche and BadFlash -

    First Aquaarche. That link I provided in my post has a lot of good information that talks about surface area available with stone versus mesh versus dumped packing. I think stone works fine but doesn't have a lot of void space and so is prone to plugging with solids. It just means it will need to be cleaned out more often but is apparently how biofiltration was done for the last 100 years before more engineered materials became available.

    The structured packing I was considering is, as you suggest, larger than 1/2". It actually has 3/4" openings. The stuff is not too bad on price and the thing I like about it is that I will sacrifice some surface area/volume ratio and end up with a larger biofilter but won't have to spend the money right away on a filter. Since my idea is to keep agitation down in the tank so that the solids tend to settle out and the I'll vacuum out the bottom periodically (we'll see how that goes) and send the solids to my conventional (dirt) grow beds. Because I don't intend to use air stones, at least at first, I won't be able to stock very intensively and hope that the trickling structured-packing biofilter will give me sufficient oxygenation to keep things happy. That link I posted a few posts up has a lot of the math associated with biofiltration area versus stocking and feeding density.

    I also decided to take the advice of someone on this board and start with "cheap fish". I caught some bluegill out of my pond and tossed them in the tank two days ago and am now just circulating the water with my ex-hot-tub pump to get a bit of aeration. We also have a grain elevator in town where I can buy a bunch of stocker-sized catfish, etc. I might do that. I hate the idea of heating the tank all next winter (or anytime).

    Wes

  7. #7
    Moderator badflash's Avatar
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    Re: Biofilter setup question

    Growbeds & greenhouses are the way to go. come winter or summer this will provide the biofiltration. The critter you chose will determine your temperature requirements. If the plants don't remove enough nitrates & phosphates, you'll need to do more water changes.
    The best fertilizer is the farmer's shadow

  8. #8
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    Re: Biofilter setup question

    Ernie, That is exactly what the aquacube is in my opinion. The structured packing is available from a guy in florida. I bought 12 ft3 for about $100. Go to biofilters.com to buy some if you want. He is pretty helpful.

    Wes

  9. #9
    Moderator jackalope's Avatar
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    Re: Biofilter setup question

    wpbullock have you got a linky to the scrubbie supplier? I'd like to see their prices and what they have to offer

    Thanks
    I use the Linux Operating System ...... Free as in beer!
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  10. #10
    Moderator badflash's Avatar
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    Re: Biofilter setup question

    Just remember with these systems, that the aquacube type filter won't remove particulates, but with growbeds it doesn't matter. If you use aerated scrubbies, they will need to be cleaned out periodically if you do not remove particulates before the water gets to them.
    The best fertilizer is the farmer's shadow

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