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Thread: Do I have algae??

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    Do I have algae??

    I have an Intex 20x48 Ultra Frame pool with a salt water system. I am very new to this and really don't know what to do...

    After a couple of storms I've notices a discoloration to the bottom of the pool. It is patches and even some lines (about 6 inches wide). It doesn't feel any different, it is not slick. I have scrubbed it nothing changes. My pool is crystal clear. You only see this discoloration in the evenings when the sun is going down about 6 or 7 o'clock. During the day with full sun you don't see it at all. Is this algae? Is it possible to have algae or mold under the pool (like between the tarp and the bottom of the pool)? I have to admit I did add 8 oz. of Algaecide, it did not make any difference. I'm a little worried now about my son getting in the pool because of the Algaecide (I'm a worrier).

    Also I am confused about my levels. I run this salt water system 8 hours a day (filter 12 hours) and my numbers are always low.

    Free Chlorine usually 0
    Total Chlorine usually 0
    Alkalinity usually 40
    pH 6.8 to 7.2
    Total Hardness 50

    As I said my pool is crystal clear, my son's skin and eyes are no way irritated like in a public pool (he wears goggles and the fill up with water and he doesn't even realize it). Are these numbers OK?

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    Mod Squad zea3's Avatar
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    Re: Do I have algae??

    What are you using to test your water? Do you have a result for CYA/stabilizer? How much salt do you have in the pool? Does your SWG have the copper ions feature?

    Please start off by reading recommended levels and Pool School.

    It is very important that you keep the pool sanitized with chlorine. The FC (free chlorine) should never drop below the recommended level. Without knowing how much CYA is in your pool I cannot tell you how high your chlorine should be.

    You must be able to accurately test your water to keep it sanitized. A high quality test kit such as the TF 100 or the Taylor K2006 will allow you to test the levels needed to maintain a safe, clean pool.

    You should not swim when the FC is 0. You may have an early algae bloom that is consuming all the chlorine the SWG is producing. For now add a 96 oz jug of 6% unscented bleach and run the pump to mix it in well. Get a sample of your pool water tested and post the results here so we may advise your further.
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    Re: Do I have algae??

    I am going to read what you said, and I don't want to sound like a total idiot, but I have no idea what you are talking about...

    Let me explain. I wanted a pool, so I went to Walmart and bought it. I bought the salt water system, looked at the chart, bought the salt, threw it in and started it. My water is crystal clear. According to the book it said I needed 200 pounds of salt. Based on reviews, they said not to put that much in, so I put in 160 pounds, with the other 40 sitting in the garage. My system neither indicates low salt or hight salt levels.

    I bought some test strips and check it about every other day. Many times daily. It also came with test strips, and when I checked it with those Thursday, the Free Chlorine was at the 1 - 2 level, pH was correct, but the Total Alkalinity was low. It did come with Copper test strips, that was fine too.

    So, I honestly don't know what CYA is, therefore the is a good chance I don't have it. The only thing I have put in that pool is water, salt and 8 oz. of algaecide.

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    Re: Do I have algae??

    CYA (cyanuric acid) is also known as stabilizer. People put it in their pools in order to help prevent chlorine loss to the sunlight. In a pool with no CYA, you will lose all of your chlorine in as little as 30 minutes just to the sunlight. Pools with salt systems especially need a goodly amount of CYA because the systems just can't keep up with chlorine production without it. We recommend 60 to 80 ppm of CYA in saltwater chlorinated pools.

    Swimming in a pool without enough FC (chlorine) is unsafe. The only way to truly know what your FC level should be is to know what the CYA level is in your pool. This is explained in Pool School.

    The Temporary Pool Guide can also help you since it pertains to your type of pool.

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    Mod Squad zea3's Avatar
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    Re: Do I have algae??

    Hi, I am going to insert my answers to your post in red.

    Quote Originally Posted by krlinger
    I am going to read what you said, and I don't want to sound like a total idiot, but I have no idea what you are talking about...

    That's o.k., I'll try to compose my answers in respect to your new pool owner status. You are no idiot, just uninformed. If we say something that puzzles you feel free to ask for clarification. Most of us are happy to help! Welcome to TFP !

    Let me explain. I wanted a pool, so I went to Walmart and bought it. I bought the salt water system, looked at the chart, bought the salt, threw it in and started it. My water is crystal clear. According to the book it said I needed 200 pounds of salt. Based on reviews, they said not to put that much in, so I put in 160 pounds, with the other 40 sitting in the garage. My system neither indicates low salt or hight salt levels.

    O.K. that sounds reasonable.

    I bought some test strips and check it about every other day. Many times daily. It also came with test strips, and when I checked it with those Thursday, the Free Chlorine was at the 1 - 2 level, pH was correct, but the Total Alkalinity was low. It did come with Copper test strips, that was fine too.

    Test strips do a poor job of telling you what is in your water. First they are inaccurate in detecting the volume of chemical in the water and the "range" they give you for results is not precise enough to be useful for adding needed chemicals to the pool. For example, if you need 4ppm of FC daily and the color block on the strip says 1-3 is pink, 4-6 is violet, and 7-10 is purple. However the color on the strip when you try to test shows something with pink/purple mottling. So is it 3 or is it 7 or is it somewhere in between? If you can't really tell then you would be guessing how much chlorine you need to add, or in your case, if you needed to increase the output on the SWG. That is why we like the TF100 and Taylor K2006 test kits. They are both high quality test kits that contain an FAS/DPD test for FC that is very accurate. With that test you count the drops until the water clears to find the FC level.
    I am not familiar with test strips for copper, so I do not know how accurate they are. Someone else can provide some information for that. Did you get any salt test strips? They are not 100% accurate but should be good enough since precision is not as critical with salt levels.


    So, I honestly don't know what CYA is, therefore the is a good chance I don't have it. The only thing I have put in that pool is water, salt and 8 oz. of algaecide.

    You would have had to add the CYA so your level is 0. For a pool your size you would need 4lbs of CYA (also called stabilizer) to raise the CYA to 63ppm. The CYA will protect the chlorine so it will last longer and sanitize the pool before the sun burns it off. You can buy CYA in liquid or powder. Liquid is more expensive of the two. If you buy the powder, put it in an old sock and tie it in front of the return flow from the pump and let the powder dissolve. You can squeeze the sock after it is saturated to speed up the process if you want. Repeat until all 4lbs have been added to the pool. Keep the pump running until all the CYA is dissolved. You can swim while adding the CYA. Once added it may take up to a week for CYA to register on a test, so go ahead and assume the full amount is in there.
    Can you tell us what brand of algaecide you put in the pool? Some algaecides contain copper and you already are adding copper with the SWG. Too much copper causes staining on pool surfaces. The good news is you do not need copper to sanitize your water. If you choose to do so you can disable the copper ionizer on your SWG. Let us know if you ever want to do that and someone here can walk you through it.


    I used The Pool Calculator to find the amount of CYA for your pool. You can use the pool calculator to see how adding different chemicals affects your pool. Your recommended level for FC is 1-3. You want to keep the FC on the high end of the range so there is enough present to fight any organics that enter the pool.

    As for the question that brought you here, try rubbing a chlorine tablet on the stain. If the stain lightens then it is organic in nature and will fade over time once the FC level is high enough on a consistent basis. If the stain does not lighten then you will need to take a sample of water to the pool store and ask them to test it for metals.

    I don't know how much longer your swim season is or if you plan to keep the pool up over the winter. We may have some additional advice depending on the weather patterns where you live.

    I hope this is helpful. Please let us know if you have any other questions or need more information.
    TFP Moderator
    Helpful links: TF Test Kits,TFP Pool School, PoolMath
    Vogue 21' round AG, Pentair 1 hp 2 speed pump, 36 sq ft DE filter, Hayward S180T 150# sand filter, Houston, Texas
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