What size water pump do I need? (RDWC)

I'm going to be running 6 5 gallon buckets with a 15 or so gallon res. So I will be dealing with around 30-40 gallons of water. What is the guideline for full cycles per hour? Some guy told me I need 700gph, seems a bit excessive, but I don't know. What do you guys think?

No idea at all? There is not that much info out there for these systems. Lots of ideas on how to build one but not much practiced theory or system specific guidelines, oh well I'll figure it out myself and share what I find.

I'd like to know the answer to this one myself. In your case 35 gals at 700gph would be 20 times an hour. 3 minutes a lap. That doesn't seem excessive to me, but what do I know?

On the other hand, assuming RDWC requires stones in every pot, which is something else I'm not sure of, the stones would keep the water agitated, so why rush it?

From what I've seen a 700 gph pump is gonna need a 1/2 horse motor. Probably 3-4 amps. If a little trickle pump gets the job done you could save some on the elec bill.

NorCal, if you decide to go the high speed route I saw 1/2 horse 650 gph pumps all obver E-Bay today for about $50. Whether that's overkill or not I do not know .......

i runn 700gph on my flood and drain set up but its a 4x8 tabel with a 350liter res oh and its only 60 or 65watt pump floods tabel in about 3min give or take

Pntrbl, airstones are a must in every container. That is something I know.

Doesn't all this really come down to how many spray heads and what gph they are rated at? I'm not really sure just wtf rdwc means but the systems I've seen have sprayers in connected buckets, these sprayers are rated at gph so the math shouldn't be hard although there are other factors to take into consideration such as how much piping there is.

uhh.. i dunno but in my DWC my AIR* pump is the 1000 one.. works great.

DONT GO FOR THE WALMART FISH AIR PUMPS. thats like 60-120... Order it online the 1000-1600 ones.. WILL EFFECT YOUR PLANTS GROWTH AND SIZE. I HAVE WITNESSED

NorCalTransplant said:

Pntrbl, airstones are a must in every container. That is something I know.

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Thanx for clearing that up for me NorCal.

It seems the thread is drifting off into air pumps. I thought we were talking about water .....

dbkick said:

Doesn't all this really come down to how many spray heads and what gph they are rated at? I'm not really sure just wtf rdwc means but the systems I've seen have sprayers in connected buckets, these sprayers are rated at gph so the math shouldn't be hard although there are other factors to take into consideration such as how much piping there is.

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Sprayers have nothing to do with RDWC systems. I have seen sprayers used in some DWC systems but they are primarilly used in areoponic systems.

pntrbl said:

Thanx for clearing that up for me NorCal.

It seems the thread is drifting off into air pumps. I thought we were talking about water .....

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From what I have gathered, bigger is better on both accounts but there has to be a point of diminishing returns. The sweet spot is what we are looking for and it seems the only way to find that out is through practice with ones system. Problably will go with a 700+ mag pump for the water and a medium sized commercial air pump my grow shop sells for aeration.

I will share what I have learned through trial and error,first thing you have to consider is what size line you are going to use to connect them togeather.my first attemt was with 4 buckets,a 400 gph pump and an 18 gallon tote as my res,and 1/2 tubeing conecting it all togeather.it filled the first bucket to fast and ended up over filling,so I put a ball valve on the line between the res and the first bucket,it worked but not what I was aiming for,so I added another set of 3/4 inch lines from the out end of the first bucket to each bucket and back to the res. so what I have is a 1/2 feed line with a total of 1 1/4 inch out and back to the res.I still have the ball valve to control flow and for quick res changes,my first grow with it is just in its first weeks and so far all is well,I dont let my ppm go over 1000 and my ph between 5.5 and 5.80 still tweaking it a bit with the timeing on the pump,so just remember to have a larger line out than you do going in and a ball valve to control the flow and it should work.I built mine because it was a pain in the ass taking care of single buckets,checking ph and ppms and res changes and crawling around on the floor,it sucked.so now I have everything up on milk crates,something you may want to consider when you have to do a res change cuz water wont flow up.I hope this bit of info helps you out and good luck

Thanks for the tips man, +rep!

Hey NorCal what size pump did you go with? I'm trying to put together a RDWC/Undercuurent design, using 1" flexible tubing to connect the bottoms of the buckets to the bottom of the controller. I will the use 3/4" tubing to connect the pump which will feed into the top of the controller. Gravity will then flow into the buckets.

A lot of the RDWC guides seem to use 250-350gph pumps. If you think about it, regular DWC does fine with no flow. So I assume any flow is better than no flow. Unless you need the flow to really mix the solution to add oxygen, any size pump should work. I think I will go with either 250 or 350gph. I will have airstones in each bucket too, so I don't need super fast flow.

This is what I'm thinking of putting in my 4x4 tent

With air pumps bigger is always better, with water pumps in an RDWC that is not the case. If you get to large of a pump you will create too strong a current. The strong current will pull your roots into the pipe causing clogs, or cause root damage. I am running 10 5-gallon buckets with an 18 gallon epicenter. I use a 500GPH Mag-Drive pump, and it works perfectly. So you definitely don't need anything bigger than that, maybe even one size smaller.

Also just FYI, your calculations on how much water you will have are pretty off. My 10 bucket system + epicenter holds 40 gallons of water. The buckets may be 5gallon buckets if full to the top, but in a DWC you don't fill to the top. Each 5 gal bucket in reality will only hold about 3 gallons of water.

I wouldn't go BIG big because if your return lines are small like 1/2 inch or whatever the feed lines will pump water faster than gravity can drain it, and then you will have flooding problems. I use 1/2in feed lines and 3/4 return lines on a 260 gph pump with zero problems! +Rep Please! Good Luck!

In an RDWC system, you will want the entire volume of water to change once every 1 to 2 hours. The simple formula is the ( total number of gallons of water) divided by 2 (hours) = necessary GPH pump. I personally divide by 1.5 because I want a little more volume exchanged.
In your case 40 gallons total in the system divided by 2 hours = 20GPH. In my case, I have 110 gallons in the system divided by 1.5 hours....so I would use a 75GPH pump. Fortunately in most RDWC systems, one is not really lifting the water, so head height calculations are not necessary.

EmeraldBuddah said:

I wouldn't go BIG big because if your return lines are small like 1/2 inch or whatever the feed lines will pump water faster than gravity can drain it, and then you will have flooding problems. I use 1/2in feed lines and 3/4 return lines on a 260 gph pump with zero problems! +Rep Please! Good Luck!

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Dude... Thank you. I just bought a $400 system like a jack ass and its just having 100 problems. This wa one that appeared suddenly. Ecerything seemed fine for the first day or two then bam, starts getting backed up and flooding. 2 bucket system with a 900gph water pump, lol. It was theonly one they had. 3/4 inch feed and 1/2 return as well.

Thatsbrutal said:

Dude... Thank you. I just bought a $400 system like a jack ass and its just having 100 problems. This wa one that appeared suddenly. Ecerything seemed fine for the first day or two then bam, starts getting backed up and flooding. 2 bucket system with a 900gph water pump, lol. It was theonly one they had. 3/4 inch feed and 1/2 return as well.

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just so you know, you replied to a 10 year old post.
welcome to riu