Sand or Cartridge Filter for New Pool

[Toybuilder]

Hi All,

We're about to sign on the dotted line for a new inground pool. The builder has offered a choice of either a sand or cartridge filter. In our first pool, we had a cartridge. Water was very clear but it was somewhat of a pain to clean.

Have never dealt with a sand filter. Anyone out there have experience with both? Is it true the water clarity isn't as good? I like the simplicity of sand but just not sure. Can anyone tell me about backwashing? How often you backwash and for how long? Is there sand "maintenance"? Replacement?

Thanks for any input. Can't wait for Spring!

[CarlD]

I had a cart for 3 years in an Intex donut, then a sand filter in my current pool for the last 12 years.
Sand filters are probably the easiest filters to maintain.
First, your sand filter should have a noticeably greater capacity than the pump. I have a 200 lb sand filter and a 1HP Hayward SuperPump and the filter is barely adequate. A 250# filter would have been better. Luckily, I have a 2 speed version of the pump and it works better on low speed. (get a 2 speed or VS pump). The slower your flow rate, the better the filter works.
Second, TECHNICALLY, a sand filter doesn't have as fine a filtering as either DE or a cart filter. But that can easily and CHEAPLY compensated for by using skimmer socks and adding a little DE (like 1/3 cup) to your filter after you backwash. Less than $10 worth of DE powder has lasted me over 3 years now...and $10 of skimmer socks should see you through a season. Both help your sand filter do its job.
Third, you backwash when your pump pressure increases by about 5psi. If you pre-plumb it into a drain, you merely turn the pump off, swing the multi-valve lever to backwash and run it till the water in the sight glass runs clear. Then turn it back to filter. Simple. Usually takes less than 5 minutes every few weeks.
Fourth, unless you add something really bad to your pool (nothing WE would suggest), you NEVER have to change the sand in your filter. As the sand gets older and "dirtier", it actually filters BETTER than new sand. It's because the wear and the locked-in dirt REDUCES the size of the spaces in the sand, catching more stuff.

My water is crystal clear, and so is that of most of our sand filter owners. Old sand, DE, big enough filter for the pump, skimmer socks and you'll get GREAT performance!

[BigDave]

I'm with CarlD on this - I love my sand filter. That said, there are fans of Carts and DE here as well. The most important thing is to size the filter to the pump - the next size bigger filter and the next size smaller pump than commonly suggested is a good start.

One thing to add to CarlD's post is a rinse between backwash and returning to filter will prevent a plume of dirty water returning to the pool.

[Watermom]

Another vote for sand. Also one more tidbit ----- when you initially fill your filter with sand, do a quick backwash before putting it on filter.

[Toybuilder]

Thanks CarlD. I don't think we'll be able to backwash to a drain but it's something I'll inquire about. That would be the best setup IMO. However, if I'm backwashing onto grass/shrubs or trees, will DE hurt them? I'm assuming some of it comes out during the backwashing.

Found the skimmer socks and they are pretty cheap as you mentioned. Does one size fit all baskets? How often do you change yours?

[Toybuilder]

Thanks BigDave. Can you elaborate on what you mean by "rinse"? Is there a "rinse" position on the valve?

[Toybuilder]

Thanks Watermom. Out of curiosity, do you add DE into your filter also? Does everyone? What does that do to the warranty of the filter? Do I dare tell my builder?

[CarlD]

1) You don't have to use DE
2) You only use a little bit, just enough to raise PSI 1lb.That usually means 1/4 to 3/4 of a cup.
3) DE shouldn't hurt your grass, but it will kill many kinds of bugs.
4) It won't affect your pool's warranty, but may affect the filter warranty, but shouldn't as it won't damage the filter.
5) I would not tell the builder. Not his business.

[Watermom]

I do sometimes add DE but not routinely. You can read more about adding DE to a sand filter in the following thread:>

http://pool9.net/de-test/

I cannot imagine how adding DE would affect the filter negatively. Filters are made to trap debris. Basically, DE is just debris that is caught by a sand filter just as any other debris would be.

[Toybuilder]

Thanks everyone for your very helpful input. Went ahead and told the builder to go with sand. However, I noticed that he will be installing the largest filter available for a Pentair Triton II, the TR-140C. which will need 925lbs of sand (really??). The pump will be a Pentair Intelliflo VS pump and will have an attached spa. The pool capacity will be ~16k gallons. He explained that we needed the larger filter because it’s the only one rated to flow the amount of water that we need for the spa to function properly. The spa only holds ~850 gallons. Does this sound right? I think I’m going to need more than 1/3 of a cup of D.E.

I will be anxious to try D.E. but I think I'm going to hold off and see what it looks like without it. I will add the skimmer sock immediately once we're up and running.