Sump size VS return pump size.

[tyler1503]

Hello R2R! I was hoping someone could help me with my sump issues.
I'm still in the stage of getting things together for my new build. I have everything already, I'm just not sure if everything will work together or if I need to purchase some new equipment.
My question is, is it possible to have a sump that is too small?
I only have a 20gal display so the stand is quite small. The only standard sized tank that will fit is a 5gal and I can't afford to have a custom built sump.
I've had a pump laying around for a while that I want to use as a return, but it's 3600L/hr (approx. 950gal). I'd at a tap to reduce the amount of water it moves and T it off to a refugium.
The overflow box can handle that amount of water (it's designed to be used with this specific pump) so will the water just flow through the sump as usual? Or is there any issues with oversized pumps in small sumps?
Thanks!

 

[lion king]

Pump size is determined more to the tank size, not necessarily the sump. That's a lot of flow for a 20g tank. Sump size has to be large enough to handle all the water from the overflow of the tank when the pump is off.

 

[tyler1503]

Pump size is determined more to the tank size, not necessarily the sump. That's a lot of flow for a 20g tank. Sump size has to be large enough to handle all the water from the overflow of the tank when the pump is off.

Total water volume is closer to 50gal so it's about 19x turnover per hour. Minus head loss it's probably closer to 16-17x. Plus I'll be dialling the pump back a bit with a valve even further. I speculate I'll have between 10-15x turnover for the total water volume per hour.
My main concern is with all that water moving through such a small area, will there be any risk of flooding assuming everything besides sump size works in my favour. But to be honest, how often does an entire build work in the reefers favour? Haha.
I could possibly fit a 12" cube tank in there, but that will be a pain in the butt to turn into a sump.

Working out how much room I'll need in my sump for when the pump is turned off is something I've completely forgotten about. Thanks for reminding me!

 

[Shaddow_wolf169]

As long as your OFB can handle the amount of water pushed through it will be fine. I'm worried about stirring up your whole tank all the time. I would definitely baffle the return line nozzle to create less flow.

 

[ifarmer]

You dont need thst much turn over.
I think 2-3 % turn over ratio is good.
On my 50g tank. I use a mag drive 3 pump as my return pump.

 

[tyler1503]

As long as your OFB can handle the amount of water pushed through it will be fine. I'm worried about stirring up your whole tank all the time. I would definitely baffle the return line nozzle to create less flow.

My ofb can definitely handle the flow. It's designed to be used with this specific pump. I'll definitely be using a valve to lower the flow

You dont need thst much turn over.
I think 2-3 % turn over ratio is good.
On my 50g tank. I use a mag drive 3 pump as my return pump.

2-3%? Do you mean 2-3x turnover? 2-3% is nowhere near enough for me haha

 

[Shaddow_wolf169]

You should turn you tank at least 10x an hour.

 

[johnwick]

10X max. Look for a pump that's around 450 gph and you'll be set. You've got waaay too much as it stands

 

[Shaddow_wolf169]

I have a 125g and I turn mine 16-18x an hour.

 

[tyler1503]

So far I've seen as little as 2% all the way up to 950 times that amount. I guess you all have success your way, so I can't go too wrong being in the middle somewhere as a starting point

But I have a feeling I may not have worded my question properly. I'm not asking what amount of flow is best, I'm asking if that specific amount of flow could bring on the potential for a flood that could otherwise be avoided by having less flow. It's quite a lot of water passing through a small area. Keeping in mind I will be dialling that flow back quite a bit, but I'm not sure how much. Just what suits the tank when the time comes.

I know I don't *need* that much flow, but if I can utilise the pump I already have, I won't have to blow my budget on a new pump if the one I have can work.

But now I'm curious, what are the pros and cons of such little flow through the sump?

 

[Frop]

I don't know the specific but my nano has some really low flow on the refugium. I can't tell you a number but it sucks, lol. Basically my tank was hardly sciphoning so the return was matching the sciphon. The return is some $10 thing rated for 100gph (~12 gallon total system size) and I use to limit that even... (until I moved the refugium lower then I upped the return to max). So I didn't literally flood my DT. I always figured if you had a filter sock upping the flow would help screen stuff out. Depending on your setup maybe more water contact in the sump is good? In my case it's mainly chaeto and a heater.

 

[FishGuyBri]

Basically if the problem involves blocked lines, your flood will be whatever is in your sump. The higher the flow, the quicker it will empty the sump. Since Murphy says this will happen when you're not home, then it won't matter.

You see, either your tank will overflow if the drain is blocked, your sump will overflow if the return is blocked, or your pump will shoot all water out of the sump if the return breaks somehow. So without knowing details, all scenarios cause a leak about the size of your sump plus five-ten percent of your tank volume (as the lines settle and levels stabilize).

The only difference the pump makes is that the stronger the pump, the faster it will empty your sump on the floor or the faster your sump will empty into the tank and overflow the tank IF that's where the problem is

 

[AZDesertRat]

Your biggest issue would be heat, with a pump that big and water volume that small you will never be able to dissipate the heat it generates. The next is velocity through the sump, a 5G sump will hold about 2.5-3 gallons of water and at even if you cut it back to 450 GPH with a ball or gate valve on the discharge side that means the sump is turning over every 20 seconds.
A 5G is not a practical sump. I usually suggest a return pump that does 3-5x the display volume or in your case 60-100 GPH. This allows some detention time in the sump for a protein skimmer to do its job, for micro bubbles to off gas and for detritus to settle out in the sump where it can be vacuumed out easily. Make up additional turnover with energy efficient powerheads/wavemakers that create little heat and move a ton of water for a couple of watts electricity.

 

[tyler1503]

Thanks for the replies everyone!
I looked into a custom built sump and it's considerably cheaper than I expected.
Plus, I measured my available space and I can fit a real sump behind the stand, but not inside.
It's amazing what ideas you come up with when you actually think haha.

 

[FishGuyBri]

Thanks for the replies everyone!
I looked into a custom built sump and it's considerably cheaper than I expected.
Plus, I measured my available space and I can fit a real sump behind the stand, but not inside.
It's amazing what ideas you come up with when you actually think haha.

haha good thought- You know, through this hobby, I often think... that i AM thinking... only to find out I'm quite clueless to many things. Thank **whoever you want to thank** for R2R or I'd have given up.