sump return pump GPH?

3 to 5 times the display volume is the most often recommended flow rate for a return pump. 75x 3 to 5 = 225 to 375 GPH.
This number is also dependent on the size of your sump, you don't want 10x the display volume going through a 10G sump, the microbubbles would be a killer.

 

Agree with this - 6 to 10 times tank volume. Frankly, the higher the better. The more flow, the more efficient your skimmer, heaters, etc. will be.

 

+1

Also, if your flow is too high, most of the water will be returned to the DT before it has a chance to be skimmed, filtered, etc which defeats the purpose of having a sump.

 

How so?

How much flow we want through the sump is one thing. You do have to supply the equipment in it with a proper amount. But moving water through a sump for the sake of moving water through a sump is a huge waste of energy and adds needless heat to the system.

 

You want lower velocity, ie GPH, so you lessen the chance of carrying microbubbles back to thedisplay plus things like the skimmer and reactors work better since they can get multiple passes of thesamewater over and over. 3-5x is a good number and you make the rest up in the display with very energy efficient prop pumps like Evolutions, Tunzes, Vortecs or Voyagers or a closed loop which is barely visible if at all.

 

Think of it this way, the worst efficiency for filtration items in a sump or for things like dosing, heating, etc., is when you have zero flow. The best efficiency is when they are sitting inside the tank (equivalent to infinite flow through a sump).

If you have too slow a flow through the sump then your skimmer is effectively over-skimming the sump water and so is not efficient. Your heater is effectively over-heating the sump water and so is not efficient.

Yes, there is definitely a point at which you reach diminishing returns and I'm not suggesting anything dramatic like running at 30 or 40 times tank volume, but I've seen a decent difference in skimmer performance from when I've run at 4x to when I've run at 10x on the same tank.

Very subjective as to the improvement, but it certainly poured out more stuff after I upped flow.

 

Efficiency is simply a matter of how much work you get out of the energy you put in. So it really does not apply to flow through a sump.

With a skimmer you are correct. A skimmer can only process so much. It can be run wet or dry, but where ever you want it, it is a setpoint. So for a 90g tank I doubt there are any skimmers out there doing more than 300 gph... more like 250 for one rated around 1.5x of a 90g. So if you give it less than that 250, then yes you will be "recircing" that water... skimming it more... but that does not effect the efficiency of the skimmer, it is still doing the same thing... but what it is not doing is processing as much of the tank as it could be.

Now if you give it 300 gph, then it is doing all it can do. Processing as much as it can. If you give it 500 gph to work with, absolutely nothing changes... it is still only doing 250 gph.

A heater itself is very efficient. Darn near all the energy put in comes out as heat. Obviously if it is just sitting in a bucket it will reach set point and turn off. So it needs flow to heat the tank... but a 300W heater means it will put out 300 watts per hour. It takes very little water flow to remove 300 watts of heat per hour. That 300 gph from the skimmer is PLENTY... only one watt per gallon per hour.

So obviously, we need flow to the equipment in the sump.... but anything over what that equipment needs is just a waste. For your typical 90g... say 100 gph for a fuge that is split off, 300 gph for a skimmer, throw 100 gph in for giggles, and you are still at that 4-5 times tank volume per hour which is plenty.

Using a return pump for water movement in a display tank is indeed very innefficient. You use a lot of energy pumping it against gravity from an open sytem and you get very little flow in return. You add a lot of heat from the return pump for very little water movement. Power heads are much much better at water moved vs. power consumed taking gravity out of the equation.

...uhh. Sorry. I must be bored.

 

I disagree wholeheartedly, however...

You support what I'm trying to get at with this statement.

This is somantics now... If I run 1 gph through a sump for a 90g tank, my skimmer is doing next to nothing to support the tank. If 2, 3, 4, 10, 50, same thing. So in limiting sump flow you are limiting the efficiency of the skimmer. It is doing the same work that it always does, but you are getting less out of it. That is low efficiency.

It's not quite as simple as that. Just because a skimmer pumps 250 gph does not mean that if you pump 250 gph through your sump that you're getting maximum efficiency out of it. Because the skimmer gets its water from the sump and it also dumps water back to the sump, the 250 gph going through the skimmer includes some new and some already-skimmed water. The lower the flow, the higher the amount of re-skimmed water is going through again. You will ALWAYS have re-skimmed water going through your skimmer until you hit a theoretical infinite flow rate. As I mentioned previously, at a certain threshold you hit a point of diminishing returns. I've found 4x tank volume to be below that threshold and 10x to likely be above it.

Again, running 300gph through a sump that has a skimmer pumping 300gph from/to the sump means that skimmer is not working at peak. If your skimmer is pumping 300gph through it and you're pumping 300 gph through the sump, roughly half the water at any given time in the sump is recycled skimmer water.

If you double the sump flow rate to 600 gph then the skimmer is sucking up 2/3 new and 1/3 recycled. Take it to 900 gph and it's 3/4 new to 1/4 recycled. You get the picture.

So come to think of it, flow rate based on display tank size is largely irrelevant. It should really be based on the flow rate through the skimmer. I think I just found my topic for my first post on the Marine Engineers blog...

I don't disagree. Don't know how that entered the conversation.

 

Well we are talking about efficiencies, so it matters. Again, we can measure efficiency across a component or across the system. So if we are going to address efficiencies, then we might as well throw in the losses you incure from moving too much water throught he sump. It is a huge loss with gravity. So OK, we can be pudent and make sure we send enough water to our equipment, but your point of doing it is to boost efficiency. Yet you loose a lot by doing that too much... and you did say the more the better.... which is not the case depending on how you want to define it.

 

A skimmer does not do its work in one pass at the water. My wife's tank is the same size as mine and is fed the same as mine. Her return flow is 10% of mine and the skim the levels are the same.

The only thing that matters to the skimmer is that you're adding enough organics in X time to keep the sump concentration above its removal threshold. That can, theoretically, be accomplished with 2 gallons of flow an hour.

There are good reasons to up flow (and good reasons to keep it down), but it does not make sense to me that more efficient skimming would be one of them.