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Thread: Algae issue with Saltwater pool / DE filter

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    Algae issue with Saltwater pool / DE filter

    Hello All,

    Went away on a 2 week vacation and let the pool go and have been facing an algae problem now for 2-3 weeks. I have a large (36k gallon) inground concrete pool with a salt system and a DE filter. All of my levels were ok - except salinity was low. I added salt and shocked the heck out of it with liquid chlorine and added an algaecide as per my local pool store's recommendations. I then noticed that the filter's pressure was way high and the flow was minimal. Next, I opened the the filter and thoroughly cleaned the elements - they were all gunked up with Algae. 24 hours later the pool is looking a much lighter shade of green/blue and the algae is (visibly) much better under control...but the filter pressure is high again. I read that algae can clog a filter in 2-3 hours. Will be cleaning the filter again tonight.

    If all levels are good, and algae is visibly getting better, is it now just a matter of letting the filter run and cleaning it every day or so to get rid of all the dead algae it is gathering? Or is there some way to better deal with what algae is left...dead or alive?

    Any further advice is appreciated.


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    Re: Algae issue with Saltwater pool / DE filter

    I do not have a salt pool but I would recommend a copper silver ionizer.
    One company I have dealt with...Chlorine in Canada florida

    silver copper ionizers will solve the problem.

    hope this helps...good luck

    James Bailes, M.D.

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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Algae issue with Saltwater pool / DE filter

    Welcome to both of you to the Trouble Free Pool Forum.

    The reason for the algae bloom is that the Free Chlorine (FC) level went too low relative to the Cyanuric Acid (CYA) level. In fact, it may have been low to begin with though the low salt level would lower the rate of chlorine production from the saltwater chlorine generator (SWG) making the problem worse. I also suspect that the pH rose during that time as it does with most SWG pools. If you do not already have one, I strongly suggest you get yourself a good drop-based test kit including a "count the drops" chlorine test (FAS-DPD) such as the Taylor K-2006 you can get at a good online price here or the TF100 test kit from here. The latter kit (the TF100) has 36% more volume of reagents so is comparably priced "per test" and Dave gives outstanding customer service.

    Take a look at this chart in the Pool School where you can see that the normal 1-3 ppm FC with 60-80 ppm CYA recommendation from SWG manufacturers is insufficient to prevent algae growth. If you follow the chart, your pool should not get green algae.

    As for using a metal ion system (silver/copper) that drjames proposes, that is not normally recommended on this forum because, as you discovered, chlorine alone can not only prevent algae (if maintained at the appropriate level), but can clear an algae bloom as described here. That link will give you more information on clearing your pool which will occur on its own if you maintain a shock level of chlorine and clean the filter as you are doing (you might look into using a skimmer sock as well). Don't forget to brush the pool surfaces. You did not need to use the algaecide that the pool store sold to you. Metal ion systems can have side effects such as staining of plaster surfaces and coloring blond hair with a green tint. Copper does kill algae, but so does chlorine and the chlorine doesn't have the side effects.

    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Algae issue with Saltwater pool / DE filter

    Welcome to TFP!

    DE filters are particularly prone to clogging during algae outbreaks, and can sometimes need backwashing every hour or two. You need to check them regularly and backwash as needed. Cartridge and sand filters are somewhat better, typically going a day or more, but you still need to check the filter pressure frequently during an algae outbreak and clean or backwash as needed.

    If the algae is all dead, then you just need to give the filter time to clean up the water, backwashing/cleaning as needed. The trick is being sure that all of the algae is dead. If you have a FAS-DPD chlorine test (included in the Taylor K-2006 and TF Test Kits TF100) you can check to see if the FC Level remains the same overnight. If it remains the same overnight, then all of the algae is dead. If you don't have that test kit it is often best to keep the FC level up at shock level for an extra day or two just be sure. You don't want the algae coming right back in another few days.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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