Changing to a smaller impeller

I have a Hayward powerflo LX 1.5 hp pump, the water flow is way to fast for my sand filter, I have looked the pump model up and they make impellers all the way down to a 1/2 hp. What would be a reasonable size to drop to? I was thinking maybe 3/4

How do you know the flow rate is too fast?

Also, what size is your filter and what is the current filter pressure?

Was the pump sold with the filter?

But I believe with the Powerflo LX, you can only drop it to a 1 HP which would still be ok.

Mas985, I have a real long thread over at the balancing water forum. I bought the pump new off eBay and got sand filter on Craigslist. Sand filter is a Hayward s200. I run 17 psi on filter, recirculate. And 10 on backwash. Psi never goes up. Started with algae, killed it but best guess is pump pushed dead algae through filter to fast to filter it out. Got a cloudy mess now. Watermom and Ben has been giving great advise. In short though the return flow to the pool is very powerful so I'm looking to slow it with smaller impeller or a shut off valve between pump and filter and close it enough to slow the flow. I saw impellers for this pump down to 3/4 but maybe 1 hp would help

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Started with algae, killed it but best guess is pump pushed dead algae through filter to fast to filter it out.

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One thing to keep in mind is the typical sand filter will filter down to 30-40 microns or so and some dead algae is actually smaller than that so it can be pushed through the filter without much effort. Some people have used DE in their sand filters to help capture the smaller algae. Have you tried that?

As for the pump, a quick calculation and my guess is that the flow rate is not much beyond the design rate of the filter (44 GPM). Maybe as high as 54 GPM but certainly not enough to cause any damage.

A smaller impeller may help but as I mentioned before, there are some things a sand filter just can't remove without a little help.

If you want to see if a smaller impeller would help, one idea would be to add enough head loss to slow the flow rate down to around 44 GPM. If you have a return valve, you can try closing that until the filter pressure reads above 22 PSI. That should result in a flow rate less than 44 GPM. If the algae still makes it through the filter, it is probably too small for the filter to capture but again, DE might help with that.

Also, can you post a link to the 3/4 HP impeller? Just want to make sure it is for that model. Not all Powerflo's use the same impeller.

mas985, the part number I saw was spx1500F says it will fit on the sp1580. I ended up adding a valve between pump and filter, half way closed my pressure reads 8-10 psi, so my pressure drops instead of rises to 22. and my water flow slowed quite abit into the pool

That should give you an idea of how your filter will operate with a smaller pump (impeller). I can't guess how close, but the same direction - maybe mas985 can give you a better idea. If you do like it then definitely change the impeller to save on electricity.

The filter pressure I gave you is for when a throttling valve that is after the filter. So using a valve before the filter, you want the pressure to drop to around 11 PSI and then the flow rate should be lower than 44 GPM.

The spx1500F would be a two steps down but it still may not be below 44 GPM although probably close.

ok, that makes sense. The one I installed yesterday is between pump and filter, and its running between 8-10 psi. I think I will hold off on the impeller change and see if this will help me. I hope to get some DE to add today and see if it will help. When adding the DE do I remove the skimmer basket and pump basket or just skimmer basket?

The DE should be fine enough to pass through the baskets.

DE is a powder. It will go through the skimmer easily.

Ok, thanks. I couldn't resist checking the sand, and sure enough, the sand I blew out on initial backwash caused me to be low on sand and the sand that's in there isn't anything like the old I took out, the new was more like play sand. I wanted to remove my lateral assembly but on my s200 the variflow comes in on the side and I couldn't get the bulkhead fitting off. Best I could tell laterals look fine. So with proper sized filter sand and some DE I hope to get my pool clean

BTW, the DE will serve two purposes, it cleans the pool better but it also will add head loss to the filter and slow down the flow which should also help clean better.