Green Pool Help :-(

[scrapgabbie]

Hi everyone! l'm hoping somone might be able to point me in the right direction... please be gentle though, l am a complete newbie and have no idea of chemistry at all :-(

We have a 11600 gallon above ground pool with vinyl liner. This is our second swimming season, and we're right in the middle of a hot Australian summer. Our pool is stubbornly green, wavering between deeper green and a pale turquoise, and l just can't seem to beat it.

l have been testing almost daily with the test kit that came with the pool, as well as dip sticks that l bought from our local hardware store. The tests kept showing:

chlorine (above 3 on the test tube test, it doesn't go any higher than that)

total chlorine (on the dip stick test) 1-2ppm

free chlorine 1ppm (dipstick test)

high ph (7.8 but l have just today got it down to 7.4)

total alkalinity 120ppm (dipstick)

total hardness 350ppm (dipstick)

cyanuric acid maybe 50 (l'm guessing here, l thought it was higher, but my eyes are playing tricks on me now and the dipstick looks better this time than it did a few hours ago.

This was the pool yesterday, it's about twice as green as this today, and darker towards the bottom of the pool.

We haven't vacuumed much this year, but l have ordered an automatic pool vacuumer which should arrive tomorrow. l'm hoping it will get some of the settled stuff off the bottom and improve things.

We don't use the pool cover, (too lazy to take it on and off LOL) but after reading here a bit l'm starting to think we should be, to protect the chlorine?

Do l need to add more chlorine, is it as simple as that? l initially thought l had too much but now l'm not sure.

2 days ago l threw a bottle of algaecide in, and nothing happened

We have got solar heating, and the pool is generally around the 25 degrees celcius mark during the day.

What is the difference between stabilised and non-stabilised chlorine?

We are in the middle of a severe drought, so can't drain the pool at all. (we are backwashing regularly, but that's it) l'm not even sure if l need to drain it though, my head is spinning trying to work out why the green won't go. Today is the first day in about a week of green that l've been able to get the ph relatively normal, but l don't know what to try next, there are so many factors that seem to influence each other and l feel like a juggler dropping all the balls.

Yes, l could go down the pool shop, but l wanted to take this on as a personal challenge LOL!

[chem geek]

Add chlorine to get the Free Chlorine level to 40% of the CYA level, which if 50 ppm CYA is correct would be 20 ppm FC. You could use a lower FC, but it will take longer to clear the algae if you do. You need to maintain that FC level adding more chlorine as needed to do so and if you've really got algae then it will consume a lot of chlorine initially. Before you add the chlorine, you can lower the pH to around 7.2 as it will make the chlorine more effective (since adding chlorine will raise the pH). You should use unstabilized chlorine for this -- such as chlorinating liquid. Cal-Hypo is also unstabilized, but will increase Calcium Hardness (CH). You only measured Total Hardness which isn't the right type to measure, but your CH is probably in the neighborhood of 200-250 ppm so if you can't get chlorinating liquid then you can use Cal-Hypo instead (it needs to be pre-dissolved in a bucket of water before adding it).

Because you have a vinyl liner (and in general, it's good practice), you must add the chlorine SLOWLY over a return flow.

Though this link shows a sequence that is more extreme on pool opening, your pool should go through something similar using chlorine to kill the algae.

The above method is the least expensive approach, but it is not the only one. If you have your water measured for phosphates and it's high, then you can use a phosphate remover to starve the chlorine, but this can get expensive. Another approach is to use an alagecide that contains copper, but that can have side effects of producing green water when the pH goes up (and green hair with blonds).

If you use the chlorine approach, then you want to maintain the high FC level until all three of the following occur: 1) the water is crystal clear, 2) there is minimal drop in FC overnight (< 2 ppm FC if at 20 ppm FC), 3) there is minimal Combined Chlorine (CC) < 0.5 ppm.

To accurately measure chlorine, CYA and other levels you need a good test kit. Get the Taylor K-2006 (shown here) if it's available in Australia or another test kit that uses a FAS-DPD chlorine test which is the one where you add some powder to make the water turn pink/red with FC and then add drops and count them until the water turns clear, then add another reagent to turn pink/red with CC and then add more drops until it turns clear again. The test kit you get should also test for pH, Total Alkalinity (TA), Cyanuric Acid (CYA) and Calcium Hardness (CH). The K-2006 will do all of that.

After you get rid of the algae, you need to maintain an absolute minimum FC of 7.5% of your CYA level so if 50 is accurate that means never letting the chlorine go below 3.8 ppm and it would be best to target 5-6 ppm FC so you don't accidentally get too low in chlorine level. If you feel you cannot do this, then you will need to use a weekly PolyQuat 60 algaecide to keep away algae in which case a lower FC level will be OK.

What kind of algaecide did you throw into the pool with no result? Another possibility for green water is copper, but your description sounds more like green algae, especially if it's more of a cloudy green rather than a crystal clear green.

Richard

[scrapgabbie]

Thankyou very much Richard, l will try all of the above today and will report back to let you know what has happened. l've already added the dry acid, l just need to buy more chlorine, which l willbe doing this morning.

l've thrown out the bottle from the algaecide, but will check today when l'm at the shops to see what it had in it.

And it looks like l need to buy a new test kit - l will check some of the online pool shops in australia and will post some links, maybe someone here could check the suitability of them if you have time :-)

thanks again!

Gabbie

[chem geek]

Gabbie,

I don't know if this link will ship the Taylor K-2006 to Australia or what it would cost. Same with the TF100 from tftestkits.com here. Either kit would be fine. Hopefully you can find someone in Australia carrying a FAS-DPD chlorine test kit. Let us know when you find one.

Richard

[ANG]

If your water is still green I would recommend trying any product with at least 96% sodium bromide, ex: Yellow Treat or Yellow Out. Just make sure you follow the instructions and at least double shock the pool after the treatment is finished.