How to size sand filter?

[dstarr62]

Greetings,
Now that I have my pool off of Baq and sparkling clear thanks to the BBB method, I want to start addressing some of the other issues that have bugged me since I've had this pool. And number one on my list is the filter.

I have a 32 ft round doughboy AG pool, 52" walls, which according to my calculations is a bit over 24,000 gals. The filter is a Doughboy Media Master sand filter, 2.0 sq ft with a 225 lb capacity coupled to a Doughboy Powerline 1.5 hp pump. This pump/filter combo literally "blows" the water right through the filter. You should see the flow at the return. I have never been able to vaccum without vaccuming to waste, stuff just goes right through the filter!

Another interesting thing about the Media Master filter is it contains no laterals. "The tank’s Single-Part Underdrain Assembly assures maximum longevity because this unique design has no laterals which can break off"
Now while this may indeed assure maximum longevity, I can't help but wonder if it doesn't also lead to mimimum filtering!

I know one of the most common filtering problems is too much pump for the filter, and 1.5 hp probably is a little on the high side, but I'm wondering if I don't also have a little bit undersized filter for my pool. According to the Hayward site, their Pro series filter that is 2.2 sq ft is rated to turn over 21,000 gals in 8 hrs. They don't have a 2.0 sq ft in that series, but I'm guessing it would be somewhere around 18,000 gals in 8 hrs if they did. That would put 24,000 gals somewhere in the 10 + hr range with a correctly sized pump.

All of that is a long way to get to the main question...since my filter is probably undersized for my pool, and my pump is definately oversized for my filter, and replacing both the pump and filter isn't really in the budget, would there be any downside to replacing my filter with one that was better suited for the 1.5 hp pump, but might be a little bit oversized for 24,000 gals? Also, any recommendations on size filter? I'm thinking something around 3 sq ft, am I on track?

Thanks for all the help from the great people on this forum!
Don

[duraleigh]

Hi, Don,

That's a pretty easy one. You simply cannot buy a filter too large for your pool or pump....bigger is better.

Since you've got a good grasp on flow rates, capacities, etc., the easiest way to select a new filter would be to calculate your pump gpm first.

Once you get that ( from the manufacturer's info), then look at filters that are rated say around 25% higher than that. So, if your pump gpm is around 60gpm, chose a filter that is at least 75 or so.

I have not seen a sand filter without laterals.......my thinking would be similar to yours. Perhaps the Doughboy folks would be helpful with some technical info.

[dstarr62]

Thanks for the suggestion, Dave. I'll have to do some digging to try and find the paperwork that came with the pump, Doughboy doesn't have the GPM rating listed on their website.

Don

[duraleigh]

Don,

You may have to call them. You need the "pump curve". It compares gpm to the TDH of your system. mas985 is the guru on TDH, but if you can find the pump curve, you would get pretty close to the GPM by assuming about 30 for the TDH of an AG pool...perhaps a little less, but I'm guessing.