Newbie, based in Italy, with green algae problem

[OliveGrove]

Hi, new to this forum and in need of help. Our pool is 4 years old, and each year it has been a bit of an experiment getting it going for the summer.

We are in Southern Italy and much of what is talked about here is like a foreign language to me. Our pool is 8 metres by 25 metres, with a .8 metre shallow end and an 2.8 metre deep end. There is no "shelf" the gradient is constant. It is in infinity type pool, and so does not have conventional skimmers. There is also a 40,000 litre "holding tank" for the overflow.

We shocked the pool about 4 weeks ago with 50 kilos of dichlor, and followed up a week later with another 20 kilos. When we first put the 50 kilos in a few hours later the pool surface looked like a frozen lake, which we skimmed off, filtered overnight, and then backwashed. The 20 kilos later seemed to clear the pool, although it was dirty at the bottom.

Last week we tried to clean the bottom of the pool, which stirred everything up and gave us very murky water, which has subsequently gone a very bright almost flourescent green. I checked the chlorine level this morning and it is about 1.5, and the PH is around 72/73.

Help!!

After reading this article turning-your-green-swamp-back-into-a-sparkling-oasis-t4147.html it seems our mistake was not clearing the bottom of the pool during shocking, does that sound right?

 

[danivdp]

Yes, and you aren't finished shocking. Shocking the pool is not just one or two additions of chlorine, it's keeping the chlorine level high (how high depends on your CYA level) until your pool is perfectly clear, doesn't lose chlorine overnight, and you don't have any CC.

Do you have a pool cleaning machine that runs all over the bottom and picks up the dirt down there?

 

[jblizzle]

It is best to clear out everything you can when you start shocking. Although, based on your description, it does not sound like you actually followed the shocking processed and instead just added some chlorine a few times.

You should read through Pool School a few times. And learn the correct way to shock a pool here:
pool-school/shocking_your_pool

The other thing (and perhaps the most important) is that you never mentioned your stabilizer (CYA) level. This is a MUST HAVE piece of information to accurate determine the amount of FC to add to shock you pool.

Unfortunately, you state that you have now added 70 kilos of dichlor which contains CYA ... therefore you stabilizer level just keeps going up making it very difficult to clear the pool. {IGNORE THIS ... calcs were based on only the holding tank ... According to poolcalculator, your 70 kilos of dichlor raised your FC by 970 and your CYA by 882 These numbers are astronomical (normal CYA is < 100 with FC < 15) and there must be a mistake somewhere. }

What are you using to test? Are you able to get the Taylor K-2006? Are you ale to get liquid chlorine over there?

 

[jblizzle]

OK ... new math based on a total pool volume of 400,000 liters:

70 kilos of dichlor raised your FC by 97 and you CYA by 88

The most concerning thing is that the recommended level of CYA is 30-50ppm. You have now added 88ppm to what ever the level in your pool was previously (and I am guessing it was not zero if you have used dichlor in the past).

You really need to come up with a full set up testing numbers ... although based on the info we currently have, a 50%+ pool drain and replace is probably recommended to regain control of the water chemistry.

 

[OliveGrove]

It is best to clear out everything you can when you start shocking. Although, based on your description, it does not sound like you actually followed the shocking processed and instead just added some chlorine a few times.

You should read through Pool School a few times. And learn the correct way to shock a pool here:
pool-school/shocking_your_pool

The other thing (and perhaps the most important) is that you never mentioned your stabilizer (CYA) level. This is a MUST HAVE piece of information to accurate determine the amount of FC to add to shock you pool.

Unfortunately, you state that you have now added 70 kilos of dichlor which contains CYA ... therefore you stabilizer level just keeps going up making it very difficult to clear the pool. {IGNORE THIS ... calcs were based on only the holding tank ... According to poolcalculator, your 70 kilos of dichlor raised your FC by 970 and your CYA by 882 These numbers are astronomical (normal CYA is < 100 with FC < 15) and there must be a mistake somewhere. }

What are you using to test? Are you able to get the Taylor K-2006? Are you ale to get liquid chlorine over there?

We calculate our total volume of water to be 440,000 litres.

At the moment I use strips of "Aquachek" which measures pH, free chlorine, total alkalinity and stabilizer. We also have a pool tester kit with two chambers of water, into which you put phenol red in one side to measure the pH, and DPD no 1 in the other side to measure the chlorine. With this the pH reads about 7.2 and this morning the chlorine I know was pretty low at about 1.1 mg/l.

I don't know about the Taylor K-2006, and liquid chlorine here is very weak. We would need tankers full of it - I did ask once, but it would not have been practical.

I will go down to the pool now with my little strips, and report back with the results, as they seem to give more of the information you need.

PH between 6.8 and 7.2 - not very clear
FC 1ppm - I know this is low
TA 120 ppm
Stabilizer 100 ppm

Down here they are great believers in stuff called "anti-algae" but I have been led to believe that if your pool chemicals are correct you should not need it. Is this correct?

 

[OliveGrove]

You really need to come up with a full set up testing numbers ... although based on the info we currently have, a 50%+ pool drain and replace is probably recommended to regain control of the water chemistry.

Problem is what do we do with 200,000 litres of water?

 

[OliveGrove]

Down here we can only get dichlor or trichlor, so I am guessing it is not the same formula as in the States. Will pop over and see what it says on the label. Dicloro 56% IMP T10KG.

 

[chem geek]

It doesn't matter what the concentration of the Dichlor is. For every 10 ppm Free Chlorine (FC) it increases Cyanuric Acid (CYA) by 9 ppm. This is due to the chemistry of the Dichlor molecule, not any separate mixing of chlorine and CYA since that's not how it works. Are you saying that you only have Trichlor and Dichlor and have NO other sources of chlorine available at all? Not Calcium Hypochlorite (Cal-Hypo)? Not chlorinating liquid or bleach? Both Procter & Gamble and Henkel have bleach products in Italy. See this link for one example of chlorinating liquid which in Italian has the ingredient "ipoclorito di sodio" which means sodium hypochlorite. It is also sold from some vendors in Italy on eBay as shown here.

 

[OliveGrove]

Thanks for those links - I will go and explore them. All the pool chemical shops I know down here have dicloro or tricloro, which are 56% and 80%, and a liquid chlorine which is only 10%, so we would need a ridiculous amount for the size of our pool. The tricloro has anti-algae in it, but it is in tablet form, which we can't use as we don't have conventional skimmers.

When I go to the first link it won't let me add anything to the cart for some reason, I think they only sell to traders. I will point the Ebay one in the direction of my husband.

Armed with this information I will also go to our supplier and ask if they can get it for us. Many thanks.

 

[jblizzle]

The first thing we really recommend is getting a "good" test kit. The strips just do not prove to be very accurate. I would hope you could find the Taylor K-2006. Really the key is to have a FAS-DPD test for your chlorine levels. Odds are that your CYA may be well above 100 as many test kits max out at that level. This will make it very difficult to keep your pool under control. Here is another problem with your test kit. Assuming, your CYA is only 100, you need to maintain your FC between 7ppm and 12ppm on a day to day basis. Since you have algae, the require shock level to maintain is FC > 39ppm. I am correct that your current test only goes up to about 5ppm? How can you maintain these levels if you can not test for them?

You are correct if you have your CYA & FC levels well adjusted, you should NEVER have to add any algaecide or other "magic potions"

You really need to understand the relationship between your stabilizer and chlorine. I would again suggest reading through pool school, but this described the various chemistry (not the CYA/FC chart):
pool-school/pool_water_chemistry

Continuing to add dichlor or trichlor is a loosing battle that seems to have been set up to make the pool store wealthy. They are designed in such a way as to require more and more of it to try to counter the stabilizer that is added which never leaves the pool unless you drain and refill ... may not be what you want to here, but it is a fact. The only other way to remove the CYA is through a Reverse Osmosis treatment ... is that something available to you?

I also want to point out that many people here in the states use household bleach (6%) as their only source of chlorine as some areas do not seem to carry the higher concentrations. Your 10% is more powerful than many here can even get, although other areas of the country have 10% and 12.5% available.

You are also correct ... to clear you pool (through the shock process) takes A LOT of liquid chlorine. However, once it is under control the amount of liquid chlorine required becomes more manageable.

Feel free to ask as many questions as you like, and we will try to give you all the help we can. However, without good trusted test results it becomes hard to give advice.

 

[jblizzle]

Just did the conversion and a 115,000 gallon pool is on the large side.

I wanted to add another option, have you considered using a saltwater chlorine generator? With a large enough system (or multiple cells), it could provide all your FC. Although realize, it would not be enough to clear your pool initially, and getting a handle on the CYA level is a must before the SWG could potentially take care of your chlorine demands.

 

[chem geek]

Thanks for those links - I will go and explore them. All the pool chemical shops I know down here have dicloro or tricloro, which are 56% and 80%, and a liquid chlorine which is only 10%, so we would need a ridiculous amount for the size of our pool. The tricloro has anti-algae in it, but it is in tablet form, which we can't use as we don't have conventional skimmers.

If the "anti-algae" in the Trichlor is copper ions, then that can stain plaster surfaces. As for the % Available Chlorine, that only tells you the weight of chlorine you will need, but not its cost. Sodium hypochlorite chlorinating liquid is mostly water and is far less expensive per its weight so ends up being roughly the same price per FC after accounting for pH adjustment chemicals as shown in the thread Cost Comparison of Chlorine Sources.

Nevertheless, given the large size of your pool, it would probably be worth getting a saltwater chlorine generator.

 

[OliveGrove]

OK, so I have read quite a bit of the pool school now and this is what I have surmised so far:

The strip test scale reads to 300 CYA and has two further increments on at 150 and one at 300. The latest strip test reading is just over 100, so for normal operation I need to raise the chlorine level to around 12, and 39 to shock. Removing a large volume of water is not feasible at the moment.

If I do raise the level to 39 to shock how long must we wait before the pool is safe to swim in?
Will constant back washing and topping up gradually bring down the CYA levels?

 

[jblizzle]

The strip test scale reads to 300 CYA and has two further increments on at 150 and one at 300. The latest strip test reading is just over 100, so for normal operation I need to raise the chlorine level to around 12, and 39 to shock. Removing a large volume of water is not feasible at the moment.

Assuming the strip is accurate (this could be a large assumption ... no chance if getting the K-2006?), and your CYA is a little over 100 (call it 120 to be safe), then your normal FC need to be maintained between 9 and 15 according to the poolcalculator. For the shock value, poolcalculator states 28 (should work) while the chlroine/CYA chart would put it above 40 (more aggressive). If you keep it over 30 that would be effective, but a little high might be faster.

If I do raise the level to 39 to shock how long must we wait before the pool is safe to swim in?
Will constant back washing and topping up gradually bring down the CYA levels?

Generally it is safe to swim in the pool up to shock levels for you CYA level. Given the discrepancy between the recommended levels, I would suggest only swimming with FC below 30. Although if you are actively shocking to clear algae, I would not want to swim in it.

You are correct that backwashing and topping off with slowly bring your CYA level down ASSUMING you stop using dichlor or trichlor which would continue to add CYA to the pool.

 

[OliveGrove]

I have not so far been able to locate a K-2006 without ordering from USA. Will keep trying. In the meantime we will be going to get a vast amount of liquid chlorine on Tuesday (tomorrow is a Bank Holiday here), and have definitely decided to stop using the dichlor. Never really used much of the trichlor as we don't have conventional skimmers to put it in.

We have people coming to stay in three weeks, is it feasible we will be on top of the problem by then?

Will do the overnight drop test as best I can with my limited test facilities, and report back the readings.

Thanks guys for all your help. Now - back to school.

 

[Butterfly]

Hi OG and welcome to the forum

Can you post a pic of your pool for us? :-D

 

[OliveGrove]

Hi OG and welcome to the forum

Can you post a pic of your pool for us? :-D

Just sent son down to take a photo.

 

[OliveGrove]

Taken with two different cameras.

 

[jblizzle]

If the pool is still green there is no reason to do the overnight test. That test just confirms that everything is dead ... if it is obvious there is still stuff living then you can wait to do the test.

Just try to maintain above your shock fc level as consistently as possible.

 

[chem geek]

I have not so far been able to locate a K-2006 without ordering from USA.

See if you can find a Palintest Pooltester SP 315C test kit. It will do everything you need except that the chlorine test is DPD. I think they only sell their FAS-DPD test in the U.S. though you can ask them about that.