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Thread: Black algae, low FC with a SWG

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    Black algae, low FC with a SWG

    My pool guy tells me to drain. But I am too nervous for that, plus, water is water and with proper treatment it should be fine. I tested today, the water is a tad hard, but ph and total cl ok, but the FC near zero. cYA ok too. The phosphates 1000 ppb. So do I just need to get a good cl shock? And if so, which one? I think my pool is about 25k. It's roughly 20x 40 odd shaped with beach entry. Thanks!!
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Re: Black algae, low FC with a SWG

    Welcome to TFP!

    Go ahead and post your test results to include FC, CC, pH, CH, CYA, and TA. Disregard the phosphate readings. They are virtually irrelevant with a properly chlorinated pool.

    Have you read Pool School?

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    Re: Black algae, low FC with a SWG

    Yes...I read it, very useful. I just retested the water and interestingly the FC is much higher than I saw earlier, making me wonder about the reliability of my testing .... Total hardness 500. TC 3. FC 3. pH 6.8. TA 180. CYA 50. The water is clear, and the bottom type is pebble tec. My pool guy started mentioning small black algae spots that brush off when he cleans. He wanted to drain and replace the water, but he has always struggled with chemistry.he says the calcium hardness is very high but I don't have that measurement. In e winter he would add cl, and wouldn't rely on the SWG. I definitely want to fix without draining.
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Re: Black algae, low FC with a SWG

    I don't see any reason to drain right now. Your CH may be higher than normal, but it is probably below 500 since that is what your total hardness is. Many folks can operate a pool with much higher CH levels than that.

    Are you running a SWCG?

    A CYA of 50 would mean that you need a minimum of 4 ppm FC at all times, with 6 being optimum. Of course, if you are running a SWCG, then this would be different.

    Your pH needs to come up. Is there a way that you can aerate and allow the pH to rise to at least 7.2. With your TA as high as it is, it shouldn't take long.

    Have you considered getting a high quality test kit? You really should make that purchase as it will save you lots of trouble down the road. Pool store numbers are very often lacking. Consider going to www.tftestkits.net and purchasing a TF-100 or a Taylor kit. The TF-100 is a better value.

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    Re: Black algae, low FC with a SWG

    I have the dipstick test. My pool guy has a higher end test. I can get the exact numbers from him. I can bring up the ph with sodium bicarb right? Yes I am running a salt wcg. How can I get rid of the small black algae specks?
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Re: Black algae, low FC with a SWG

    Ok...he says the calcium hardness is over 1000ppm. Could this be allowing the algae to grow? If so how do it fix it?
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    JasonLion's Avatar
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    Re: Black algae, low FC with a SWG

    If calcium is 1000 that would be a problem, but that doesn't have anything to do with algae.

    Earlier you said that total hardness was 500, and calcium is part of total hardness, so one of those numbers must be wrong.

    It would be a huge help if you have your own test kit and could get reliable numbers.
    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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    Re: Black algae, low FC with a SWG

    I do have my own test kit, just doesn't have the calcium test. Turns out he hasn't run the calc test in months, so I am certain my TH number is correct. There is scaling and he said that the ph is 6.8 because he dumped a buttload of acid last fri. It was 8.2! So I think that the high ph and TA has caused the scaling and isnt allowing the FC to keep the algae gone. Plus it is black algae. Here is my plan. I am going to go down on scuba and scrub the ba with a wire brush Then shock the pool with a calc free shock. After that, I will readjust the ph and TA. If the TH is still a bit high I can drain 25 percent at that point. How does that sound?
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    dmanb2b's Avatar
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    Re: Black algae, low FC with a SWG

    Test strips are un-reliable at best. You should strongly consider investing in a test kit that can with repeated accuracy measure FC, CC, PH, TA, CH and CYA.

    As others have mentioned, the TF100 from Tftestkits.net is a great value and the Taylor K2006 is good too.
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

    Pool School, TFTestKits, Pool Calculator

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    Re: Black algae, low FC with a SWG

    I ordered a Taylor k2006. My pool guy has this kit as well and he did the testing on my water yesterday. Here are the numbers...CH 600, TC 3.0, FC 3.0, pH 7.8, TA 180. He added 1/2 g acid, retested 15 minutes later TA 120 and pH 7.4. I learned that the white flaky scaling floating in the water is most likely coming from the salt cell...that the higher pH levels (he said it has been over 8) make this happen. I let him know how important it is to keep that pH down...anyways, the other problem of the small specks of black algage remains. He brushed it with a wire brush each week but it grows back. The pebble tec doesn't make complete removal easy. So, do you guy think I should go down on scuba, and really scrub the heck out of each spot, then chock with a non cal hypo shock? I want this ba dead! If you think this is a decent idea, is a sodium dichloro shock ok to use? Thanks so much for the help
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Mod Squad Bama Rambler's Avatar
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    Re: Black algae, low FC with a SWG

    You need to shock and brush if you have black algae. One thing you've left off your tests that is really important is CYA. What it it? without knowing we can't tell what your shock level is.
    Dave J. TFP Moderator
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    Re: Black algae, low FC with a SWG

    Sorry...CYA 50
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Re: Black algae, low FC with a SWG

    I know I need to lower ca and TA and brush and shock for the algae. The lowered ch and ph should help the scaling. What sort of shock should I buy and how much for a 15000g pebble tec in ground? I know cal hypo is a no. Sodium dichlor? Should I buy tricolor tablets and rub on the alage spots
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    JasonLion's Avatar
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    Re: Black algae, low FC with a SWG

    Dichlor adds CYA, which I don't think you want right now. The best way to add chlorine is with liquid chlorine or household bleach (unscented no special features).

    If you really have black algae, then yes rubbing them with trichlor is a good idea. First double check that it is really black algae. Black algae normally forms rounded spots, which can be partially scraped off with a fingernail, and when that material is rubbed on paper it leaves behind a green smear.
    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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    Re: Black algae, low FC with a SWG

    Thanks. The ba is small black spots. I'll scratch it tomorrow to see if it looks green. I got mhnew Taylor kit... Thanks for the rec it is great. Here are today's numbers:
    Fc5
    Ph 7.8
    TA 120
    CH 430
    CYA 38
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Re: Black algae, low FC with a SWG

    Since I want to drop the ph soon and not wait for service thurs, what sort of acid? For my spa I use granules but I am guessing not for the pool? And after I brush the ba, using liquid cl to shock...how high do I need to bring the FC up to for effective black algae killing? I really appreciate the help!
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    JasonLion's Avatar
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    Re: Black algae, low FC with a SWG

    You can use dry acid (sold as things like PH Minus) if you already have it, but we recommend using muriatic acid. Muriatic acid is available at most hardware stores and is much less expensive than dry acid. It also doesn't add anything you don't want added, while dry acid adds sulfates (which aren't a huge problem but can occasionally get to high enough levels to be a minor issue).
    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

  18. Back To Top    #18

    Re: Black algae, low FC with a SWG

    Great! And how high to I need to bring FC with bleach to kill the acid? And should I buy a calcium hardness reducer?
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    Re: Black algae, low FC with a SWG

    I meant how high do I need to bring the FC to kill the ALGAE. I have read 10ppm. Also, I was looking into algatec algaecide which is sold in a 64oz bottle. But I can not find anywhere how much to add for a 15k pool.
    20x44x8 Cardinal vinyl IGP, 33000 gal, 2 hp Mustang, 60 SF CrystalWater DE, Zodiac LM3 SWG

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    frustratedpoolmom's Avatar
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    Re: Black algae, low FC with a SWG

    You don't need algaecide. I would say raise your FC up to 16. The trick to killing BA is to brush it frequently to knock the heads off. You don't need anything but chlorine and elbow grease.

    Don't worry about your CH for now - as long as you keep your PH 7.6 or lower with Muratic Acid you should be able to prevent any problems associated with the high CH.
    Helpful links: Pool School; CYA/Chlorine Chart
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