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I only have 12" head pressure because the sump is behind the tank on it's own stand. I'm a bit high on the flow side but I don't have too much in the way of micro bubbles.

I'm just wondering if my skimmer would pull more sludge if I somehow slow down the flow?

The way I roughly calculate mine is that with my Rio 32HP pump rated at 1300GPH at 6' head I have it throttled back to about 1/4 open via ball valves (~325GPH) with 90 gallons in the display tank I figure this entire volume should in theory pass through the pump 3+ times an hour. I have a 55G sump with ~30G of water in it, I did not take this volume into consideration, allthough perhaps I should.

Ok, so now I'm trying to guestimate what kind of turnover I'm really getting through my sump and how to throttle it back if I can.

It's a 120g (48x24x24) with a mag 7 for the return. The pump's output is 3/4", which first goes to a 1" adapter. Then it's two 1" 45's (sweep 90), then a 1" check valve and a 1" ball valve, finally adapted back to 3/4" for the gasket, then back to 1" for the pipe that rises to the upper regions of the tank, then out a 1" 90.

Basically it's going through two 1" 45's and a 1" 90, a 1" check valve and a 1" ball valve. I'm guessing I'm getting about 500gph through it so about 4x water turnover.

Would turning down the ball valve (on the output of the pump, no ball valve exists on the input) shorten the life of the pump/impeller in any way? I'm thinking that would be my simple solution to eliminating some noise.

I think I have microbubbles because ****loads of 1/4" sized bubbles cling to the nasty fiber-like that grows on the various plastic things in the tank and when I blow off the rocks with the turkey baster bubbles get blown out from the undersides of the rocks. I have no baffles in my sump unfortunately. I'm planning on getting some eventually but I'd rather upgrade to a larger sump at the same time if possible (when $$ happens).

RC has a head loss calculator if you really want to check the loss, but I'm thinking 500gph is a reasonable guesstimate anyhow.

Putting a ball valve on the output of a pump is totally fine. It's just additional head pressure. Interestingly most pumps seem to draw less power when throttled back this way, basically it's the speed of the water that seems to be directly related to consumption, not how high the water is being lifted. I'm not sure if this is true for all pumps but most pump curves that I've looked at seem to indicate this.

If the issue is noise though, I'm curious how you have the overflow setup (Durso, Stockman, etc. ?) and how the pipe enters into the sump. If the pipe comes straight down, you get this splashing effect. Sometimes lowering the pipe so that it exits just under the water surface can help. One thing I've found that makes a big difference is if you can have the pipe come in at an angle, then the water "slides" into the sump as opposed to "falls/splashes" into the sump.

You can limit the output of your pump with no ill effects. It's only when you limit the input that you start creating problems for the pump.

thanks. gonna turn it down a bit right now.

and about those filter socks for the returns, how often should they be changed?

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Mags aren't pressure rated so putting them under additional load would shorten their life shouldn't it? I killed a mag 18 in pretty short time using on a becket skimmer. Personally, I'd get baffles or upgrade the sump like you said. Another trick I use to cut down on micro bubbles is placing LR rubble around my return pump. Then I place my carbon bag on top of that.

Hmmm, mags *should* be able handle a little bit of pressure. I don't think I would dial it down past half, but it's just perceived as head pressure. They're usually awesome little workhorses. I wonder if you had a bad pump Danny? I've been running my beckett skimmer for like 4 years now on a Mag18. IME Mags usually just go and go and go. I finally threw out a mag 7 after about 10 years of use (I had bought it used in like 1998 or thereabouts) about a year or so ago, but it was because the impeller had developed a wobble, and basically had ground out the bearing hole. Ie. I couldn't just get a new impeller as the hole for the impeller shaft actually became oval.

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It very well could have been a bad pump. I was glad to get rid of it though, they aren't the most energy efficient pumps out there.

No, indeed, nor very quiet for that matter. I was trying a mag5 in my FW tank (upstairs near my TV) and the hum coming from the tank/stand was intolerably loud. I ended up having to switch it out for a Sedra pump (still not 100% better but at least it's possible to hear the TV over it!)