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  1. #1
    Members samtheman's Avatar
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    Need help selecting the right gph pump for my system

    I am using a Mag drive MD7 on my system, I am not sure if I calculated it properly for my system, I have a 100 gallon sump, three 100 gallon growbeds, and 360 gallon fish tank. the height of my fish tank is 40". The flow to the growbeds are good, but the flow of water going back to my fish tank is very little. My setup is based on a CHOP2 system. Water from my fish tank returns to the sump by gravity. The pump at the sump feeds the growbeds and the leftover goes back to the fish tank. I am not sure if I should buy a bigger gph pump or adding another pump that can pump the water from the sump to my fish tank to increase the flow of water coming out by gravity

  2. #2
    Moderator davidstcldfl's Avatar
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    Re: Need help selecting the right gph pump for my system

    Hi Sam, lots of variables ....1st, we need to look at the performance chart for your pump...
    http://www.aquaticeco.com/images/static ... es/MD2.gif
    You said your tank is 40 inches tall, lets add a little height for resistance of water going through your pipes. Say 5 ft...according to the chart, you are getting just under 500 gallons an hour. That [i]should be [i] a good starting point. ( in theory...you could be getting 125 gph in each GB, plus the FT)

    Just so we are all on the same page, here is a drawing of a chop 2 system...
    http://www.ecofilms.com.au/2010/10/28/a ... -revealed/

    Sam, whatever flow of water is 'going into' the fish tank, has to be coming out. If you have a ball valve at the fish tank and at the grow bed(s), you could cut back on the flow to the bed(s) and increase the flow to the fish tank.
    However....This will slow down the 'fill time' for the GB's...your bell siphons may not kick in, due to lack of incomming flow (?)



    Is there a problem with the fish and/or system ? or your just concerned because it doesn't look like much flow into the FT ?
    Are you concerned with the DO ? Do you have a spray bar on the water going to the FT ?
    You might consider a small air pump in the FT. If you get one with a built in battery backup, that will be an added safety measure.

    Of course, you already ran your pipes...I try to go one size bigger on the supply line, from the pump. This gives 'less pressure/resistance' and a little more flow.
    Also, keeping the amount of 90's to a minimum helps. I use 2- 45 degree fittings together, instead of one 90 degree. Yes, it's kind of overkill...but it is less resistance.

    Lots to consider...
    "Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same." - President Ronald Reagan

  3. #3
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    Re: Need help selecting the right gph pump for my system

    From my experience when it comes to pumps the gph and flow you are looking for I have always learned to go bigger. If I calulate I need 2000gph turnover, I'm probably going to look for a pump close to 4000gph as possible. You lose flow from all types of things even 90's like David said. I practice the same thing he does and use 2 45s where ever a 90 would be going.

    Not trying to get off topic, but after reading some peoples comments about Chop2 I was wondering if some things could be done different. For instance the overflow that is drained back to the sump could you not have it drain back into the growbeds?

    If you are going to have it drain back in the sump how about put baffles in your sump like saltwater tank sumps have. Have the water drain at the far end of the sump and your pump at the other far end to pump back to the grow bed and fish tank. The baffles might help trap some of the solids (just like detritus is trapped in saltwater sumps, does require some cleaning out here and there though) and you could also put some type of media between the baffles to help with further filtration. Just an idea.

  4. #4
    Members cedarswamp's Avatar
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    Re: Need help selecting the right gph pump for my system

    Hydraulically speaking the friction loss difference between 1-90 or 2-45 is non-existant.

  5. #5
    Members samtheman's Avatar
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    Re: Need help selecting the right gph pump for my system

    Quote Originally Posted by davidstcldfl

    Is there a problem with the fish and/or system ? or your just concerned because it doesn't look like much flow into the FT ?
    Are you concerned with the DO ? Do you have a spray bar on the water going to the FT ?

    Lots to consider...
    David, thanks for your quick response. I am running an air pump for my fish tank. I am not sure if I can call it a problem, is more like a concern, but it could be later on: two out of the three growbeds are filling up and draining within 16 minutes which I understand is good I think. My third growbed is filling up and draining in 35 minutes, and I did that in purpose in order to get water back to the fish tank, if I adjust my third growbed to fill and drain within 16 minutes then I get no water going back to the fish tank at all. My question is : is it good or bad to fill my third growbed in 35 minutes or is that harmful in some way?

  6. #6
    Moderator davidstcldfl's Avatar
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    Re: Need help selecting the right gph pump for my system

    Quote Originally Posted by cedarswamp
    Hydraulically speaking the friction loss difference between 1-90 or 2-45 is non-existant.
    Hi Cedarswamp, there are sevearl charts online showing pressure loss in pipes and fittings. Here is a link to one of them.....
    http://www.engineeringtoolbox.com/pvc-p ... d_801.html
    "Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same." - President Ronald Reagan

  7. #7
    Moderator davidstcldfl's Avatar
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    Re: Need help selecting the right gph pump for my system

    Quote Originally Posted by samtheman
    if I adjust my third growbed to fill and drain within 16 minutes then I get no water going back to the fish tank at all. My question is : is it good or bad to fill my third growbed in 35 minutes or is that harmful in some way?
    No set answer for that Sam....'generally', I would think once a plant is established, 35 mins wouldn't be that big of a deal. You'll have to keep an eye on the plants.
    Maybe you could slow the flow into the 2, that are filling quicker ...sending more to the 3rd and to the FT (?)

    Your 100 gal GB's 'should be' holding aprox 40 gallons of water each, due to the displacement of your media.
    If my math is correct... ...you would need 160 gph going into each bed, to fill in 15 mins. This would leave no flow for the fish tank....considering, your pump's performance chart was showing 480 gph at 5 feet of head.

    Sorry Sam.....if playing with the flow to the grow beds doesnt work, you may need a second (smaller) pump to send water just to the FT. If you get a 2nd pump, consider adding a spray bar to it.
    "Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same." - President Ronald Reagan

  8. #8
    Members samtheman's Avatar
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    Re: Need help selecting the right gph pump for my system

    Thanks David,

    I am going to play with the flow on the 2 growbeds and slow them a little bid and see what happens.
    Men!!!, It's tornado weather right now in Orlando. I am going to try it tomorrow morning.
    thanks again!

  9. #9
    Members cedarswamp's Avatar
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    Re: Need help selecting the right gph pump for my system

    Quote Originally Posted by davidstcldfl
    Quote Originally Posted by cedarswamp
    Hydraulically speaking the friction loss difference between 1-90 or 2-45 is non-existant.
    Hi Cedarswamp, there are sevearl charts online showing pressure loss in pipes and fittings. Here is a link to one of them.....
    http://www.engineeringtoolbox.com/pvc-p ... d_801.html

    Sorry I was speaking in terms of practical backyard application. The added turbulance created by the extra joints will negate any savings you realize from using the 45's. I do hydraulic calculations for my job.

  10. #10
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    Re: Need help selecting the right gph pump for my system

    Quote Originally Posted by cedarswamp
    Quote Originally Posted by davidstcldfl
    Quote Originally Posted by cedarswamp
    Hydraulically speaking the friction loss difference between 1-90 or 2-45 is non-existant.
    Hi Cedarswamp, there are sevearl charts online showing pressure loss in pipes and fittings. Here is a link to one of them.....
    http://www.engineeringtoolbox.com/pvc-p ... d_801.html

    Sorry I was speaking in terms of practical backyard application. The added turbulance created by the extra joints will negate any savings you realize from using the 45's. I do hydraulic calculations for my job.
    what kind of hydraulic calc's? just curious,, i spent some time designing fire protection systems..

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