High phosphates blamed on fertilizer

[honeill]

Most of the summer my pool has been sparkling. Then 6 weeks ago it got cloudy. I went to the local pool store and they said my phosphates were high and gave me a phosphate remover which I used and then vacummed the deposits to waste and all was good. Then it happened again about two weeks ago and after two more treatments of phosphate remover (after two more trips to the pool store for testing) my pool is still cloudy and my phosphate reading is off the charts. Pool store is blaming my landscaper and says its due to the fertilizer getting into the pool. I've used the same landscaper for years and never had this problem before. We've had the pool for 6-7 years, it's a 40 x 18 vinyl inground pool and uses a SWG with a sand filter. Pool temp is currently around 80F and I think it is around 23,000 gallons. Here are my latest readings;
Free chlorine=2.67ppm Total chlorine=2.85ppm combined chlorine =0.18 pH=7.7 hardness=77ppm
Alkalinity=55ppm Cyanuric acid=52ppm copper=0.2ppm iron=0.1ppm phosphates=2500ppb salt=3000ppm

Do I just keep throwing more phosphate remover (and $$$$) at the problem in the hope it works? I've lost confidence in my local pool store because even though I bring them a sample they can't diagnose the problem and a course of action. They tell me to put the phosphate remover in and then come back with another sample and we'll see where you are. It's a 30 minute ride each way and I seem to be wasting a lot of time and money. Any help would be great. Thanks for reading.

[chem geek]

No, you don't need to keep using phosphate remover. Chlorine can kill algae faster than it can reproduce regardless of algae nutrient (phosphate and nitrate) level IF you maintain a Free Chlorine (FC) high enough for your Cyanuric Acid (CYA) level. You have not done that. Your FC is too low. You need to SLAM your pool to get rid of algae (read Defeating Algae and SLAM - Shock Level and Maintain) and then maintain your FC level according to the Chlorine / CYA Chart. You should also get your own good test kit (see Test Kits Compared for two recommended kits).

[czechmate]

The true culprit of late summer algae start lies for the most part with the owners lack of knowledge about the CYA throwing a monkey wrench in their embedded believe, that 3-5ppm of free chlorine is just fine to ward of any algae start.
So many times I have been told by a pool store as soon as they started to test my water that my FC is too high at 6ppm. When I replied that it is on the contrary too low, the clerk would either roll his eyes or grin like if I did not have a clue. Until you check the CYA level, (which I have at 90ppm), you cannot comment on the FC needed. One time the Leslie's staff member here in Dallas got quite animated, telling me that CYA had absolutely nothing to do with a required level of chlorine in the pool.
When you getting schooled by people of this caliber no wonder so many pool owners suffer the consequences.
Algae may start slow as to the visibility to an unsuspected eye. ( There is an early warning sign though, which is a sudden slightly murky or little cloudy water, that experienced owners are on the watch for all summer).
And when it becomes clearly visible 10-15 ppm may not do the job so many owners naively expect!
To correctly determine the necessary amount of chlorine is figured only by a POOL CALCULATOR, using a CYA level tested at least two different pool stores.
Otherwise you walking into the circle known as "pay me now, or pay me a lot more later".

[honeill]

Yes they put my sample in their little machine again and said your FC is 2.67ppm which is within the 2-4ppm range and your TC is 2.85 again within the 2-4ppm range and my CYA is 52ppm which is within the 50-160ppm range, so all you have to do is bring down the high phosphates (2500ppb) and all will be good. I know something else is going on here. My initial goal is to get the pool clear again and then try to figure out how this happened and how to stop it from happening again. It's almost end of season and we're missing out on the last few days of swimming before kids go back to school. I had to tell my kids they couldn't have friends over because I was shocking the pool today.

Anyway I went to another store and they agree with Chem Geek's analysis. I have one question though, while I have looked at the chart I don't know how much liquid shock to put in. If my CYA is 52ppm is the target to get it to a Target FC of 4 by adding 24 of shock (24 what? quarts, gallons) Is there an example or notes on the FC/CYA chart I can read? I guess I still don't understand the relationship between CYA, FC, CC and TC so I can avoid this in the future, Chemistry was never my strong suit in school :O)Thanks for the help.

[honeill]

OK now I'm getting dangerous with all the info out there on the web. Here is something I found on a couple of State sites regarding CYA;

How much is too much cyanuric acid? – The Nebraska Swimming Pool Act has set the
maximum level at 100 ppm. A 2007 study by the Centers for Disease Control and Prevention 3
(CDC) revealed that cyanuric acid significantly diminishes chlorine’s ability to inactivate the
chlorine-resistant protozoan, cryptosporidium. Based on the findings of the CDC study, the
Lincoln-Lancaster County Health Department recommends that cyanuric acid levels not exceed
30 ppm.
What are the effects of higher levels of cyanuric acid? – As the level of cyanuric acid rises,
free chlorine’s ability to act as a disinfectant is weakened. At above 50 ppm of cyanuric acid, the
time it takes to kill bacteria in the water is longer compared to swimming pool water without
cyanuric acid. Also, as the level of cyanuric acid builds up, the chlorine will become
increasingly less effective in keeping the water clean and problems such as increased cloudiness
and exceeding combined chlorine limits can occur.

So now I'm worried that at 52ppm my pool is a safety risk (acid and a carcinogen) and your CYA chart recommendation starts at 60ppm. Am I getting paranoid with all this info?

[chem geek]

You need to raise the FC proportionately with the CYA level to have the same active chlorine level -- the chlorine that disinfects, prevents algae growth, oxidizes bather waste (but also skin, hair, swimsuits). Having 3 ppm FC with 30 ppm CYA has the same active chlorine level as 6 ppm FC with 60 ppm CYA or 9 ppm FC with 90 ppm CYA.

So what you have read is referring to what happens if the FC is kept the same (and low -- say 1-3 ppm) but the CYA is increased. The active chlorine level (proportional to the FC/CYA ratio) gets lower. If you look at the Chlorine/CYA chart I linked to, you will see that the FC/CYA ratio is fairly constant at each CYA level.

So don't worry about the higher CYA level if the FC level is kept higher, but in practice you don't want your CYA level to be too high because IF you need to SLAM the pool with a higher chlorine level it takes more chlorine to do so.

Most pool stores do not understand the chlorine/CYA relationship even though it is known science definitively determined in 1974.

[free info]

How long are you running your pump/filter? When your water is cloudy and your shocking your pool it needs to run 24/7 until clear or it will take way to long. How cloudy was it before you added the phosphate remover? Normally when you add phosate remover it even get more cloudy has it cleared up from adding it twice closer to normal? Know just adding lots of chlorine and running your pump/filter 24/7 until clear takes along time and you want to enjoy the pool while you can so you can buy some yellowtrine powder in a 3lb container (sodium bromide) add as directed and this will speed up the process so you can swim faster. It does use up chlorine but you have a salt pool so you will be fine.
Also know your sand filter is not as good as a DE filter or cartridge filter and also makes things go much slower as the sand just doesn't catch everything like the other filter elements.

[free info]

Remember once the pool is clear your salt sysytem doesnt shock your pool so keep in mind doing this with liquid chlorine when needed.

[honeill]

I'm trying to educate myself on how best to interpret the results from the pool store tests of my pool water. From other articles and your SWG FC/CYA matrix I thought I had a plan. Keep the FC at 5% of the CYA. From your chart at 60 CYA I would need 3-4 ppm FC (5% - 6.6%). On my last test I had 52 CYA and 2.67 FC (5.1%), while within the range did not fend off an algae attack. Is there another piece to the puzzle I am missing, or was the FC level just too low. Thanks.

[chem geek]

The FC that is 5% of the CYA level assumes the following:

1) This is for a saltwater chlorine generator (SWG) pool (such as yours); for a non-SWG pools the minimum FC is 7.5% of the CYA level.

2) It assumes your FC and CYA levels are accurate. Pool store testing is notoriously inaccurate, especially for the CYA test. You can't use test strips either. What you are missing is your own good test kit -- either the Taylor K-2006 or the TFTestkits TF-100 where the latter has a greater volume of reagents you use the most so is more economical (see Test Kits Compared).

3) It assumes you don't have yellow/mustard algae. The FC/CYA level is enough to prevent green and black algae growth. Yellow/mustard algae needs a higher FC/CYA level to prevent, though usually one tries to completely eradicate it including getting behind light niches and under removable ladders since this algae prefers shade.

4) It assumes you have good circulation in the pool. If you have poor bottom circulation, you need to point your returns to improve circulation or have a higher FC/CYA level or use supplemental products. For an SWG pool, one can use 50 ppm Borates to reduce the rate of pH rise and those also act as a mild algaecide as well.