[goblin072]

I have read some on this and it seems many people recommend 8-10 times per hour.

My question is does this number decrease as the tank size goes up?

ie. A 50 gallon tank might need a high turnover rate to keep things healty.

A 5,000 gallon tank with 2 fish would not need to pump 10x or 50,000 gallons per hour to keep a few fish alive.

There has to be something more to the formulae than the standard 8-10x.

The amount of fish per gallon would have to be taken into consideration.

My 300+ tank is on the low end. It has two little giant pumps. Accounting for head they probably only push 1,500gal/hr. Thats only 5x per hour.
My tank is not heavily stocked, no corals. Just fish and inverts.

The fish are doing well, should I up my flow?

When they talk about flow do they mean just pushing water around like a powerhead or do they mean water run through a filter of some kind?

I could put a fan type water blower for more agitation.

[bguile]

When they say flow, they mean pushing water around. Many people, like me, get it confused in the beginning and think that your return pump is supposed to be doing all this moving, but it's not. That's what powerheads and the more recently used eductor/penductors are for.

Based on my own opinions gathered from what I've read on these and other forums, the amount of flow depends on a couple things:

1. The bio-load - Depending on how much life you have in your tank, you will need to be able to keep any wastes and detritus suspended in the water as long as possible so it has a better chance of being filtered out (ex. overflows, filters, etc.)

2. The structure (rockwork) - The more open your rockwork is, the less flow you need. The purpose of more flow is to get rid of dead spots and again, keep as much detritus suspended as possible until it can be filtered out. Unfortunately some people abuse this just to beat their chest and say that they have 20x flow in their tank and wonder why thier corals don't open and their fish never come out of the rockwork

3. Specific need - Some corals and fish do better in more turbulent waters with higher flow, some don't. So provide accordingly.

HTH. I'm sure there'll be other schools of thought on this but IMHO this has been most logical and seemed to work for me in the past. I had a 90G that maybe had a return of about 400gph and total 600gph in the display. I had 13 fish all under 3" and corals that I grew and fragged and sold back to the LFS for more stuff. Never had a problem.

[salt-rookie]

This sounds more like a FLOW versus VELOCITY discussion. I run about 6 X through my sump, but I recirculate via closed loops, the volume of my SPS exclusive 180 display about 70 X. The high turnover rates are mainly for the corals. I'm not sure fish really require much flow.

[Poseidon]

I am pretty close to 30X in my 90. Like was stated above though, it is not about the velocity, but the volume. I use a pair of Tunze's and 4 outputs from my basement sump.

[goblin072]

30x!

With just 5x my tank has about zero particulate in the water. Super clear water and no fish problems. As long as nitites and ammonia are zero why have more in a FO? What good would it do me to increase it?

Again just fish, live sand and inverts no corals.

[bguile]

Originally Posted by goblin072

30x!

With just 5x my tank has about zero particulate in the water. Super clear water and no fish problems. As long as nitites and ammonia are zero why have more in a FO? What good would it do me to increase it?

Again just fish, live sand and inverts no corals.

In your case none. Unless there is a spot in your tank where all the fish poop gathers that's not cleaned on a regular basis

[Poseidon]

If it works for you, then like bguile said, do nothing. I have a super heavy Acro load, so the added flow is really important to me. I have super clear water too...