Display To Sump Flow Rates?

[Tiggsy]

Assuming flow within the display tank is more than ample via the use of streams what should dictate the flow to the sump?

Is it a mutiple of display size or tank size? or does it relate to skimmer intake?

For example, i have a 110G Display and a 175G Sump system.

At present i only have a smallish skimmer (standard perc 120 unit) in the sump.....i am returning water via an Eheim 3500lph from sump to tank.

Would there be any point in uping this as the skimmer cant intake all that water as it is?

More important is when i upgrade the skimmer should i also up the flow to the sump? Part of me says yes but part says that the longer the water in the sump is exposed to the skimmer and the DSB the better- hence it will be returned "super clean" at 3500lph (which is a fair amount for a 110g tank isnt it?) or is it better going back with an extra 2000lph a lttle less clean?

[Glenn@home]

Skimmers are subject to the law of diminishing returns, there is an optimum dwell time for the water in the skimmer body after which the amount of crap removed drops off signficantly.

So i would go with the manufacturers recommendation since this is likley to be close to optimum under a wide range of conditions.

As to flow through the sump, 'depends' is about as good as it gets i think, i have heard a number of values and reasons why the flow should be such and such but nothing definitive.

Hopefully somoene will have a reasoned argument as to why the flow should be x or y.

Glenn

[Stevielad]

Ahhh - depends!

Have you read Si G's bit on reef eden - it is quite helpful.

OK - so tank to sump turnover needs to be aqequate. What is adequate depends on how much waste is produced or effectively stocking density. Having said that surface skimming will increase the ability of a skimmer to remove waste from a larger volume of water - as the waste (that a skimmer is able to remove) has a tendency to accumulate at the water surface. So effectively the higher turnover (within reason) the better - but over a given flow there will be no effective improvement.

Whatever the tank to sump turnover - the skimmer should be run with the correct pump and flow rate. So for maximum efficiency the tank - sump turnover will equal the skimmer flow rate and all water passing through the sump will be skimmed. If the tank-sump flow is higher than this you won't remove any more crud with the skimmer. It may have other benefits e.g. increased O2 in water?

Set against this is what you hope to achieve in the sump - i.e. do you need a low flow rate for waste to settle out - which is then removed by critters or simply syphoned out. Or do you want a high flow rate - which is what is recommended with MM sumps - to help macroalgae growth?