Water turnover?

[goog]

Lee,

In the "Setting up a FLOWLR" thread you reccommend 8-10x capacity turnover per hour with turnover equal to the sum of the power heads and main pump. Ideally, what would you recommend for the main pump in terms of turnover? 80% of return capacity?

I have a 180gal FO, two corner returns that flow to two sock fliters, each flow into their own wet/dry chamber. The output sump contains a ASM G3 proten skimmer (rated a 2x tank capacity). The ouput of the system pump seems very anemic (a meager 240-250 gal/hour total measured at the output, This was "proffesionally built"). The system theorectically reaches the 8-10x capacity goal due two 1000 gal/hr powerheads (no way to actually measure and quite honestly don't believe the manufacturers claim).

If I upgraded my pump to a pump that allowed me to limit flow through a ball valve and maxed out my flow based upon the limit of my returns is there any way this could be bad? It seems as though flow through the main pump should be the "cake" and the powerheads should be the "icing" flow-wise. It seems like most reccomend 5-10x flow through the main pump.

Thanks!

[leebca]

I would only 'require' or suggest that the main pump be sized to over 50% of that flow if the tank was heavily stocked. In this case, more water should be going through the mechanical and chemical filters as well as the skimmer (the skimmer should be sized up too).

So unless there are special circumstances, 50% is adequate.

The circulation has two main functions -- movement of water inside and passing water through filters. If the main pump is over-sized, you may still need inside circulation to get to all places in the aquarium. Let's see if I can make this clearer. . .

If your main pump is doing most of the circulation, you have to be sure you're getting good water movement in the tank with this pump. What is happening is that the internal tank water movement is then more dependent on the main pump and this isn't such a good thing. The main pump return is usually on the top of the tank water line. This water flow is not directed to all nooks and crannies. Putting for instance, directional returns adds to the back pressure, so typically these pipes are 'open.' So to get circulation to the other parts of the tank, powerheads are needed. In this scenario (a heavy duty main pump) the circulation may have to be 20X (main pump turnover + inside powerheads) just to get circulation to all parts of the aquarium, with the use of inside powerheads.

This is to say that there is 'wasted' main pump circulation. One of the downsides to this is that, it is the main pump which usually contributes the most heat to the system, so oversizing it should be avoided.

[goog]

Lee,

If you can picture the standard 180 (24"x24"x72)" with 2 corner returns. I usually "point" my directional returns down, trying to achieve top to bottom flow of the freshly filtered water. I aim my two power heads slightly down toward the opposite corner (sorry...very vague description). Not what I would really call an organized flow. Any suggestions?

Thanks

[leebca]

You can sort of decide for yourself. It is adequately directed water IF every inch of substrate, live rock, and decoration has water flowing on it. That is, no dead spot(s).

You really don't want dead spots, or you'll not only have areas gathering detritus, but you'll invite the dreaded 'red algae' growth that likes such areas of low to no water movement.

So from the brief description, my concern would be circulation in the middle of the tank from the front to the rear (on the substrate, live rock, decorations, etc.). I'd prefer a third return in the middle but could live with the two corners if their return was toward the center. Look for and eliminate dead spots with powerheads.