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Thread: Green Filter Sand

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    Green Filter Sand

    We inherited a pool with our new house in August. I've had trouble with algae, water will be crystal clear for awhile, I'll brush sides and bottom and see a green film arise. Pool then turns cloudy green, and I'll SLAM again. I've done this three times. Granted, I may be messing up the SLAM process, but I will meet all criteria for couple days in a row before I quit.

    The pool does need to be resurfaced so I thought rough areas on floor and walls was giving algae place to hide and make hard to kill. After my 12K-13K resurface estimate, I decided I wanted to look at filter. I did find out from guy who took care of pool for former owner that he thinks they changed changed sand 5-6 years ago.

    This past weekend, we opened filter. The freeboard was 15 inches and the manual for our model (Triton TR-60) specifies a freeboard of 10.5 inches. So that could have been some of our problems, sand loss over time. The question I have is about the sand we removed, it was greenish tint. I have a picture below of clean sand, and the sand removed. Has anyone ever seen sand like this? I was told by the former pool guy that the owners used a mineral pack system. I looked that up and it says the minerals contain copper. I'm am not doing the mineral system. The feeder is still in place but empty. I'm using the BBB method.

    Would mineral packs cause the green sand?

    Could my algae issue be caused by the low sand level. Was the green sand a problem?

    I'm currently on Day 4 of SLAM (Target FC 22 with CyA of 55). My OCLT has been zero for 3 days. The CC is zero. The water is now a white cloudy vs green cloudy and drain is visible. I still see a greenish dust stirred up when I brush however, it is more whitish than green now. I am going to continue SLAM until I don't see the green when brushing.

    The filter pressure increased 5 psig during the first 24 hrs of SLAM. I backwashed. It has increased 1 psig in 2 days. I'm considering adding some DE. Should this only be done when I need some help filtering, such as during SLAM. Or can this method be used on a normal basis, after every backwash?
    Do I need to vacuum when done if I don't see any dead algae on bottom. I'm not sure if the white powdery stuff I disturb while brushing is dead algae or pool surface coming off.
    Attached Images Attached Images
    20K IG gunite
    TR-60 Sand Filter, 1HP Pentair single speed pump
    Memphis TN

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    Mod Squad jblizzle's Avatar
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    Re: Green Filter Sand

    Low sand levels will not cause algae. Algae is ONLY caused by inadequate FC in relation to your CYA level. And the SLAM process which your are following in the correct path forward.

    You should backwash when the pressure rises 20-25% over the clean pressure. DE can help speed up the clearing process when the water is cloudy, but it should not be needed on a regular basis.

    You can vacuum whenever you want. I doubt it is the pool surface.

    I am not sure why the sand looks green, I suppose it could be due to copper. OR maybe some alternative form of sand was used that looks green?
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
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    Re: Green Filter Sand

    So the importance of adequate filtration is what? If filtering is not adequate, does that just lead to cloudy water because of small particles not being removed. But as long as my FC is right based on CyA levels, no algae should form? I'm at a loss for why algae keeps coming back on the floor of pool. The test criteria seem quite simple to follow...OCLT < 1ppm, CC <0.5 ppm, crystal clear water, no visible algae. I've been been keeping my FC in correct range religiously. My pH stays in range. Water chemistry is good.

    Where do most go wrong on the SLAM process, because I must be doing something wrong.
    Other pool owners and pool stores are telling me I need to do weekly shock and algacides, I keep telling them no, that is not needed. Start off with a clean pool and keep chemistry right and brush and filter, you should be fine. I'm working harder than they are on this pool stuff and I'm getting very frustrated.
    Could I have mustard alage that comes back after SLAM process? The algae I get isn't noticeable at first. The pool floor becomes dull looking, water dull looking. I brush and stir the algae up. I don't see clumps of algae.

    As for pool surface, I think it is pretty bad. My dolphin bag will contain white chalky material. The former owners painted pool about 5 years. Bad idea that I have to live with now.

    Thanks for comments.
    20K IG gunite
    TR-60 Sand Filter, 1HP Pentair single speed pump
    Memphis TN

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    linen's Avatar
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    Re: Green Filter Sand

    Welcome to tfp, curlytop09

    Quote Originally Posted by curlytop09
    So the importance of adequate filtration is what? If filtering is not adequate, does that just lead to cloudy water because of small particles not being removed.
    You are correct. Many people come on here with the notion that filtering alone can get rid live algae...it can't since it can't keep up with the algae growth rate in the pool, so even though it may remove some live algae when you backwash, meanwhile much more has grown in the water. In the end, most of the filters work is getting rid of dead algae when doing the SLAM process.

    It seems that you are doing the process correctly. It could be that your sand filter is not catching the dead algae and that is what is ending up on the floor. Since you have some question of you sand and you need to add more, maybe it would be good to just replace it all with new sand (we don't normally recommend this, but when you don't know the type/history of the sand, this is the easiest way to make sure you have good sand). Then if that does not start clearing the water, I would add the DE.

    Quote Originally Posted by curlytop09
    Could I have mustard alage that comes back after SLAM process? The algae I get isn't noticeable at first. The pool floor becomes dull looking, water dull looking. I brush and stir the algae up. I don't see clumps of algae.
    Mustard algae typically shows up on the walls and floor that get the most shade. How many times have you done the full SLAM process? When you say "stir up the algae" what color is it?
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Green Filter Sand

    I did replace all the sand since I didn't know history and what it was. Relatively cheap (if doing yourself) and easy to do.

    This is my 3rd SLAM. First since new sand. Each time my water has gotten beautiful. I'm amazed at how clear it can become. Then over time it gets dull but still clear . Seems each time I brush I start to see more stuff stirred up. First it is a whitish material. Then it starts to get green tint few days later. Then much darker green. Im referring to stuff i brush off floor anf walls. That's when the whole pool turns cloudy and green tint.

    Former owners kept filter on 24/7. With cooler temps and shorter days I've backed off. After one full month here, the electric bill freaked me out. I did a test watching electric meter and a full time pump is about $140 a month. I want to back off this since from what I've read, I should not need 24/7. I am going 24/7 during SLAM

    What should I check for proper circulation. Does the bottom drain ensure than the concentrations of chlorine in pool is well mixed ? Do the jets provide the surface movement to get leaves/bugs to skimmers
    20K IG gunite
    TR-60 Sand Filter, 1HP Pentair single speed pump
    Memphis TN

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    linen's Avatar
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    Re: Green Filter Sand

    Quote Originally Posted by curlytop09
    This is my 3rd SLAM. First since new sand.
    If you want, it might help if you post as you get results during this SLAM, it may show something. What test kit are you using? What test kit did you use for cya, and how long ago was that result?

    Quote Originally Posted by curlytop09
    Then over time it gets dull but still clear
    As you probably know, the minute the water looses that sparkle, it is already too late, so I would instantly raise it up to SLAM level and start the process.

    What FC level do you maintain when not slamming?

    As long as the water is moving everywhere in the pool, you should be fine for getting good FC distribution. I have used table tennis (ping pong) balls on my pool surface to access circulation.

    Quote Originally Posted by curlytop09
    Do the jets provide the surface movement to get leaves/bugs to skimmers
    Depending how they are angled.

    Quote Originally Posted by curlytop09
    Does the bottom drain ensure than the concentrations of chlorine in pool is well mixed ?
    Not necessarily, depends on the flow pattern in the pool. I am able to get great circulation though out my pool including in my deep end, with just a surface skimmer.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Green Filter Sand

    I am using the TF-100 Test Kit. I ran complete set of test prior to starting SLAM. Here was my starting point

    FC 7ppm
    CC 0ppm
    CyA 55 ppm
    pH 7.4
    TA 70 TA always runs low but my pH is steady
    CH 270 ppm

    Below are my test results with numbers given as date, time, FC, CC, amount of added 8.25% bleach after sample taken
    Added 3 gallons of bleach previous night
    10/27 8AM 21 , 0, 4C
    10/27 2PM 24 , 0, 0C
    10/28 6AM 23.5, 0, 0C - filter pressure increased my 4 psig, backwashed
    10/28 4PM 21.5, 0, 5C + had to add water (should have done before starting)
    10/28 8PM 21.5, 0, 0C
    10/29 6AM 21.5, 0, 4C
    10/30 7AM 23 , 0, 0C + no sampling previous day.. had some kid issues that took up whole day and part of this day
    10/30 6PM 20 , 0, 8C
    10/30 10PM 21, 0, 0C
    10/31 6AM 20, 0, 10C filter pressure increase by 4 psig, backwashed
    10/31 10AM 28, 0, 0C I may resample soon. This is a big jump in FC based on adding 10 cups of bleach to my 20Kgal pool

    We are expecting 1-2 inches of rain today, so not sure how that will impact SLAM process. I tried to brush pool while raining, but could not tell if anything was being stirred up because of rain hitting water. The water is still blue and drain is very visible. I have a lot of leaves right now too because of wind and rain.

    The change in FC in relation to how much I add does not always end up where I think it will based on pool calculator. What are some errors in the FC test that people make. Can you add the reagent too fast? When I know result is going to be high, I will add ten drops at a time before stirring. I do let up on the squeeze after each drop to try and keep same drop size. Other than that, the test seems foolproof. I also sample from opposite end of where I add the bleach.
    To check circulation with golf balls, what should I look for and where should I start with them in water.
    How many turnovers per day should I have in pool. Does this vary with season? My next evaluation is to estimate what my pump output is to see how long it takes to turn over pool. I found the pump curve for my pump. At minimum I'm getting 30 gpm, which is one turnover every 4 hours.

    I was asked above what I keep my daily FC at. Looking back through test log, I have kept FC between 4 - 8 ppm.

    I took the old filter sand to pool store. It is Zeosand which has the green tint to it. I do recall them trying to convince me to try that when I bought replacement sand. I didn't want to spend 2.5x on filter media when I had read mixed reviews on Zeosand.
    20K IG gunite
    TR-60 Sand Filter, 1HP Pentair single speed pump
    Memphis TN

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