mas985, I was going to lead Dennis slowly to the same direction but you just slam dunked the discussion! ;-)

If you take a kitchen sink and do lots of washing up the dirt is everywhere. pull out the plug and let the water run away, it will even form a vortex at high speed but only when the last 1/4" of water drains away to 0 does dirt on the base of the sink flow down the drain otherwise it stays put and you have to wash it away afterwards. same in a pool. you have to push the debris down the holes so the rest of the time it's circulating pretty much the clean stuff.

If the circulation via the M/D improved Dennis then your skimmer can't handle the flow, a second or third skimmer would take the strain off the pump and dirt enters from the top so taking it out before it can sink to the bottom is the best answer.

Leaves etc do stick to the walls of the pool, this is due to the boundary effect, water at the edge maybe stationary or even going in the opposite direct to the flow created by the return jets. Increase this flow with your big ol pumps and the boundary layer gets bigger so more debris becomes trapped at the perimeter.

This can again be seen in a dirty bowl of washing up water, go mad winding it around in a circle and you may see the perimeter dirt stationary or going the opposite way. Moving the water gently produces a smaller boundary layer.

It's true skimmers don't work very well on low flow, but that's again because the water needs to push the debris into the skimmer rather than trying to pull the water in. It would help a lot if there was a really good skimmer on the market but pool equipment has never needed to be efficient because if you bolt on a big enough pump, no matter how bad the plumbing water will arrive at the other end so bad design is the normal with pool equipment. I am working on a better design of skimmer as a project, it takes time and I could used some CFD software to shorten down my experimental stage.

The other point I would like to make is what is the point of the turnover rate? or what is the point of better circulation?

Chlorine kills most harmful things in seconds, they are dead and that happens if the chlorine is available and well mixed which doesn't mean high turnover or circulation. What chlorine doesn't kill needs to be filtered out but regular high rate sand filters and element filters and even DE if the rate is too high doesn't filter these out because many are too small so they just get recirculated around and around, just a waste of electricity because you are not achieving anything. Chlorine has done it's job and the rest of the dirt and skin cells etc gets broken up in the rough treatment moving through the filters that are too course to remove the other stuff.

Slower filtration is better filtration, high rate is just straining the big stuff and using lots more expensive electricity to do it.

If a Chef wants a clear consomme they let it flow through the filter slowly to produce an almost clear stock, if they applied 1 bar pressure to push it through it would come out dirty.

Quote Originally Posted by DennisP View Post

In regards to debris, only some debris will float. Only what floats will get sucked into the skimmer. Anything else that falls to the bottom will stay there,
Most debris floats at least for a while, the surface tension on the water supports a fair amount of dust, leaves, pollen etc until it gets water logged and then sinks, that is the optimum time to remove it but you can only do this if the system is running. That means if you switch off your pump at night and there is a storm/strong winds or even mild wind, by morning you'll be out there with the cleaner or robot.

We don't run our pools 24/7 because of cost. I have gone to the opposite end of the rainbow with testing this. My pool runs 24/7 the water is the cleanest it has ever been. The little dust cloud that gets pushed up when manual vacuuming, the one where the pool is clearer before you start cleaning? That dust cloud is no more because the water is moving constantly so more goes into the skimmer (downside is you have to empty the skimmer more often)
Now many people say my water is crystal clear but eyesight is bad, plenty more to come out of the water to make it really clear when tested with a turbidity meter. Now the electricity I use on my pool is 30 watts when no one is swimming, that is still enough to have the water moving and skimmer working and when swimmers are in the pool I push it to 69 watts. I can afford to run my pool 24/7 on that low level of electricity and moving water is better than stationary. The flow rate is slower but that means the filter catches more although I do use better filter media than sand (4 micron filtration but with flocculation as well to remove sub micron particles) so more of what the filter catches is not recirculated and is back washed away leaving cleaner water and using less chlorine although that is cheap anyway in the big scheme of things.

I sold my pool robot 3 seasons ago, it's not needed any more.

The pools I work on with main drains get re plumbed and I put a 3 port on them to use them as inlets unless draining or cleaning is taking place. Putting the heated water back through the main drains does wonderful things for warming up and de stratifying the water.