Pentair FNS conversion to Cartridge

IUsedToSail

Bronze Supporter
Jul 22, 2020
147
Maryland
Anyone out there have experience converting the Pentair FNS Plus to a Pentair Clean and Clear?

I've been looking at the pictures and diagrams of the two models and they are appear to be the same shell with the only difference being the internal manifolds. I currently have a 36sqft FNS which I feel is undersized, I am looking to move away from DE. My spousal unit has growing concerns about the DE getting washed into the yard because of the pets as there was some article in the NAVMA journal on the topic. Additionally I'm tired of dealing with the DE, we live in a very breezy area with a fairly open one acre back yard. Between the kids, landscaper, pets, and wind it seems to clog up fairly quickly. We go down to our beach place fairly often and I would like to be able to leave for the weekend without having to worry about whether or not the pump is working too hard or it's time for a flush. This past year I installed new grids, kept my CYA/FC nicely balanced and was getting 4-6 weeks between back flushes. I pulled it apart apart to verify I wasn't getting any algae sludge and it was always just lots of debris stuck to the DE - grass, dirt, hair, mulch etc. I've tried skimmer socks and they help to some degree but my two little boys and the dogs are just brutal.

Anyway, I don't see a point in spending $1k on a new filter that is basically exactly what I already have save a handful of internal parts. Also, I'm considering the Waterway Crystal Water 425sqft as an option.
 
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I think after you buy all the interior pieces for a cartridge filter it will cost you as much as buying the complete filter.

And note that the inlet and outlet pipes are reversed between the Pentair DE and cartridge filters. You must remove your MPV and not use it on a cartridge filter.
 
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You can reverse from a DE filter to a cartridge and back.. I wont say its a pain in the butt, but is can be a pain. I've done it with used parts, manifold, stack pipe, foot petal, orings etc. just go with the Waterway, it's a Dang good filter. I'd say waterway filters are best on the market right now for DE/Cartridge.
 
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You can reverse from a DE filter to a cartridge and back.. I wont say its a pain in the butt, but is can be a pain. I've done it with used parts, manifold, stack pipe, foot petal, orings etc. just go with the Waterway, it's a Dang good filter. I'd say waterway filters are best on the market right now for DE/Cartridge.

Thanks. I'll probably just order the Water Way filter. It's made in the USA and I've been extremely happy with their Power Defender 140 VS pump I bought two years ago. ($250 after energy rebate).
 
Okay... I've had a few folks ask about what my research has come up with. I have the FNS Plus 36 SQFT filter, which appears based on the dimensions to use to the same housing as the Pentair Clean and Clear 320 Cartridge filter. It looks like there are four parts or assemblies necessary to convert the filter.

See my spread sheet below. Surprisingly the filter media is half the cost; I didn't try to find additional cartridges by companies like Pleatco but I'm guessing this could be accomplished for a little less money. Given the uncertainty of whether or not these are actually the correct parts, I'm going to just go ahead and order the Water Way filter instead.

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didn't try to find additional cartridges by companies like Pleatco
For any future readers, a member just got pleatcos for 1/3 the cost of Pentair OEMs. Tomorrow's prices could be the other way for all we've seen this last year or two, but WORTH checking into if you ever need. :)
 
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