Flow rate, turnover, return pump, power heads... How much and where?

Lylelovett · Jul 24, 2018

Afternoon all,

I'm building my first mixed reef tank (sps down the road) and am really struggling (head exploding) trying to figure out flow rate and turnover and how much comes from the return pump vs the power heads. I've read innumerable posts on the 10x turnover vs lower turnover vs 40x turnover.

My tank is an SCA 150g, 5x2x2 with a 40g sump - which gives a grand total of 190g. I'm planning to have 2 power-heads of some kind; gph informed by livestock and size of return pump.

So these are the kinds of questions I'm struggling with every minute of every day:
- Does my return pump need to be capable of a full 10x, even if I end up running it at 5-7x range of speed?
- Do I use a slower/smaller return pump that runs full speed in the 5-7x speed range and supplement my turnover/flow with the powerheads to hit than 10x and beyond?
- It is better to buy a smaller pump that runs max speed all the time or OVER-buy and get a larger pump that runs at 75% all of the time; energy wise is that better?

My head's so full of this it makes my brain hurt. Or am I over thinking and just buy something already?

Thanks for any insight you can provide,
J

Dr. Reef · Jul 24, 2018

This might help a little

https://www.reef2reef.com/threads/how-much-flow-and-how-much-light.297801/

James Mikell · Jul 24, 2018

Always buy bigger and turn down. Less stress on the pump

hwntunda · Jul 24, 2018

Dr. Reef · Jul 24, 2018

Better to buy bigger and dial down for return pump.
For flow inside the tank maxspect gyre are good options. 2 of those units 1 on opposite end each alternative current can satisfy almost any type of reef.

madweazl · Jul 24, 2018

While Triton recommends 10x turnover through the sump/refugium, I've not noticed a difference between 3x and 10x over the past two years (I've played with everything in between and think I'm around 5x at the moment but this just because the water levels were in a range I was OK with). When it comes to the display, that return flow is almost nothing so I rely on a pair of MP40s (75g display) to create that; I have those running in anti-sync at 100% (acropora dominant).

We recently moved into a new home and are setting up a 150g that will essentially be run the same way; we'll be using four MP40s, roughly the same 5x flow through the sump (Reeflow Hammerhead/Dart remoted in the basement).

Running a lower duty factor on the pumps is always a good thing.

mcarroll · Jul 25, 2018

Lylelovett said:
10x

Lylelovett said:
40x

Lylelovett said:
10x

Lylelovett said:
5-7x

Lylelovett said:
10x

Feeling a little caught in the numbers – I get it.

Let's unpack.

You're solving two problems.

Sump flow to keep the skimmer, etc well fed is one.

Tank flow to keep corals happy and detritus lifted is two.

Sump
Gearing flow through the sump so that it can process the display tank's volume from twice an hour to four times an hour is considered optimal and has for a long time. Recent trends for double that flow are just that – recent trends. Take them for what they're worth.

Four or five times your display's flow rate is a good target if being on the low end of the range feels too weird to allow.

So at most you need around (60 gallons • 5 =) 300 GPH of return flow.

"Overbuying" or whatever is another recent trend.

A more tried and true route is to put some thought into the system and the pump selection in order to get the right sized pump for what you need. It's not even hard.

And a pump that'll do 300 GPH for your system doesn't have to cost much....a typical QuietOne, Mag or similar will do the trick.

Tank
Attaching a "_x" number to tank flow is much more arbitrary and less well founded.

Pumps can be very different from one another to begin with, so comparisons can be tricky on all levels. But comparing them on "_x" numbers or even GPH is not very helpful to the point of being almost silly.

GPH tells very little of the flow story, but it's the only real parameter we have to go by when selecting pumps we have no experience with.

Watching this vid on flow will help with some concepts AND give you a nice visual display comparison of some common pumps:

One of the main ideas to take in is that flow velocity is the main useful aspect of flow in the tank. It's the characteristic that allows flow to do the jobs mentioned – keep corals happy and detritus suspended.

Corals have a so-called boundary layer made up of mucus and the friction layer of water flowing around them. All exchange in and out of the coral has to penetrate this layer.

Detritus is constantly being pulled on by gravity as it circulates the tank – eventually it's weight will be more than the flow velocity can lift in some area of the tank and it settles. "Good flow" assures this level of flow velocity in as many areas of the tank as possible.

If the flow in the tank is of limited velocity, then the corals in the area of effect of that pump will also be limited as will the ability of detritus to be lifted.

But to speak in "_x" numbers anyway...

In my 50 Breeder I have about 8000 GPH....3000 continuous and 5000 variable. About 160x.
In my 37 Gallon I have about 4800 GPH....2400 continuous, alternating. About 64x.

Both tanks are old and pretty full and yet still get pretty great flow, predominantly from Tunze pumps. If it seemed helpful, you could start with half that flow in a new tank and build up the rest as corals grow in.

2¢