Dirt coming in through the return

[PoolOwnerT]

Hi everyone,
I hope someone can help me out. I'm sure this has been answered before but as a newbie I'm not allowed to search threads. Anywho I have a Haywood Sand Filter and recently after vacuuming and backwashing and rinsing when I put it back on filter some the dirt comes back through the return. Now this is a recent problem so I was wondering if it was an indication that I need to change the sand. I bought the house with the pool about 5 years ago and never changed the sand, not sure when the last time the previous owners changed it and there's now way to contact them. I don't even know how old the pool or filter is to be honest. Recently I had to buy a new pump cause the old one died and when we opened it up to try and repair it, it was all rusted.

I'm trying to find the least costly method of fixing this problem as we plan on converting to an in ground pool in a couple of years. Thanks

[Watermom]

Hi PoolOwnerT and welcome to the Pool Forum!

Your sand doesn't need replaced. I'm on my 11th season with same sand, one of the other moderators is on year 14 and another on year 9 I think.

Did this problem start after you bought the new pump? What size is your pool (volume), what size is your pump and what size is the filter?

[PoolOwnerT]

The pool is 15,000 gallons, the filter size is 1.5hp and it's a Hayward Sand Filter Model S-166T with 50PSI max.
I bought the new pump this season, it's the same size as the old one. It was working fine for about a month when this started happening with the return.

[Watermom]

A 1.5hp pump is big for a 15K gallon pool. It may just be pushing debris through with so much force that your filter can't catch it. How many pounds of sand does that filter have?

[PoolOwnerT]

Ok I'm reading off the filter and it says .45mm-.55mm "filter sand" 100 lbs. The pool gallon I gave earlier might not be right, I know it's a 27ft round above ground pool.

[Watermom]

I'm not the equipment guru around here but I'm pretty sure a 1.5hp pump is way over-sized for a 100# sand filter. That may be your problem. Let me have someone else confirm my suspicion.

[PoolDoc]

15,000 gallons is a reasonable figure for a 27 round pool.

However, maximum effective flow on a 16" filter is only 20 GPM . . . and your pump is pushing way more than that. But on a pool your size, you need 35 - 45 to maintain good water quality.

I don't really know the history of how AG pool filter ratings got done, but somehow AG mfgs were able to get the NSF to say that, on AG pools, you 25gpm per sft of sand surface was OK, but on IG pools, you couldn't go higher than 15 gpm. It's not like water in AG pools is different than water in IG pools, so there is some serious bogus-ness in those ratings!

In my experience, for really good sand filter performance, you need to be in the 12 - 13 GPM per sft range. On your filter, that would me around 17gpm!

Having an oversized pump and an undersized filter is a common, common problem on AG pools. You need to either:
+ step up to a 24" sand filter, OR
+ throttle your flow back to 20 gpm.

The first is a MUCH better option. If you do the second, you'll need to reload sand into your filter after you get the flow throttled. You've almost certainly blown a lot of your sand out in the backwash!