Persistent green algae, CYA 100

[joecoyle]

hi,

I've just come out of hospital (2 weeks) and returned to a green nightmare. There is a layer of green algae across the entire floor of my above ground vinyl pool (26,500 litre). My first instinct was to shock it to FC 10, which I did with calcium hypochlorite (my last batch!).

Since this did nothing after a few days, I was left with only dichlor granules to raise FC even further. I've made this mistake before (and never learn), that the CYA jumps massively with dichlor, so now am at FC 22, but with a huge CYA of 100. The algae is still present and doesn't seem to be oxidising.

I should add that my pH is perfect at 7.2 and TA is right where it should be.

According to the SLAM chart, for CYA 100, the FC level should be 39. I think this is impractical to reach, certainly with dichlor, will cal-hypo get there any faster? How much will i need to add?

The pool calculator gives different strengths (48%, 53%, 65% or 73%) for cal hypo, but i have no idea what strength mine is (doesn't say on the bucket, just calcium hypochlorite).

What about sodium hypochlorite (liquid) - i can buy that from my chemical supplier - £35 for 20 litres... that says it is 15% strength. How much would i need to sort this problem?

I've never used liquid chlorine before so am worried about liner damage etc.

Thanks
Joe

 

[Texas Splash]

Hello Joe! You have the right idea, and the best test kit available, so all I would suggest is put the Cal-Hypo and Dichlor away and stick to just the liquid. Sodium Hypochlorite. Wherever you can find it at the best price, then simply enter the correct "weight" (%) into the Poolmath calculator. From there, simply follow the instructions on the SLAM page (link below) and continue to maintain the SLAM FC until you pass all 3 SLAM criteria.

My only concern is the CYA of 100. Just to be safe, have you done the diluted test? If not, you might want to do it as shown on the TFP Pool School - CYA page, starting at Step 8 just to make sure the CYA isn't actually higher. Other than that, liquid chlorine (aka regular bleach) is the best way to maintain the SLAM FC level. Cheers!

 

[Demegrad9]

Couple more thoughts.
1. Never use any trichlor or dichlor products is CYA is already at or above 50ppm.
2. Never use any Cal-Hypo unless you know you'd like to raise CH
3. Never really had a problem with liner damage but you can pour the bleach in front of a water return jet and it'll disperse nicely preventing liner damage

Lastly, if the algae appears to have settled nicely on the bottom, you could vacuum to waste.

 

[joecoyle]

Hiya, I didn't even know about the diluted test. I've just performed it and it came out at 50, so x2 gives me 100. So my CYA is pretty high then. Still cant get my head around pouring bleach into a pool that kids are gonna swim in!! But i suppose its no different than any other chlorine based chemical! I'll have to get hold of some liquid chlorine then and just keep slamming until it goes! Thanks

 

[needsajet]

Sorry to hear about your hospital time and trust all is well.

Bleach is fine provided it is not "splashless" or "scented" and it has a % sodium hypochlorite shown on the jug. Bleach that has no number is often only 3%.

Pool chlorinating liquid also has a % sodium hypochlorite on the jug. I pay AUD15 (about GBP9) for 15 litres of 12.5% at a big-box hardware/building supply store.

You could empty out half the water and then refill which would get your CYA down to 50 and make things quite a bit easier going forward. If you need to conserve FC titrating reagent (I have to down here!) you can use a 5 ml sample when you're above 10 ppm FC, in which case each drop = 1 ppm FC.

 

[joecoyle]

Couple more thoughts.
1. Never use any trichlor or dichlor products is CYA is already at or above 50ppm.
2. Never use any Cal-Hypo unless you know you'd like to raise CH
3. Never really had a problem with liner damage but you can pour the bleach in front of a water return jet and it'll disperse nicely preventing liner damage

Lastly, if the algae appears to have settled nicely on the bottom, you could vacuum to waste.

Demegrad9, because i have a vinyl pool, CH isn't (or shouldn't !) really be an issue for me should it? My current CH reading is: 150. Normally my CYA lives around 30-50, so i should be ok to continue using tri/dichlor as a stabilised sanitiser, but i see everyone on TFP seems to prefer bleach? How do they get around it being absorbed by sunlight too quickly unless they add separate CYA? Is it more cost effective to add bleach & CYA vs tri/dichlor?

Cheers
Joe

 

[Pool Amateur]

because i have a vinyl pool, CH isn't (or shouldn't !) really be an issue for me should it? My current CH reading is: 150. Normally my CYA lives around 30-50, so i should be ok to continue using tri/dichlor as a stabilised sanitiser

Tri/dichlor contains CYA and will significantly increase CYA, which is why it is highly discouraged, Calcium Hypochlorite will add CH because you have vinyl it should be reasonable " as long as not too high" but I have not been able find what too high is or the side affects of too high are. I have read that when you add cal hypo you should disolve it 1st, then you will be dealing with liquid bleach with a lot of calcium in it. whether pouring in bleach or sodium hypochlorite 10% very close to same thing but the 10% sodium hypochloite is stronger than most bleach sold in store. The big thing is understand what it is you are putting into pool and what it does to your pool.

As for now I believe you will need to do a water replacement to get your CYA to a level the chlorine can be effective AND have the proper level of FC in the pool for the CYA level.

 

[Demegrad9]

Couple things going on here. Your CYA is normally 30-50ppm, but for some reason it's 100 now? What changed? Basically if you believe your CYA is at 50ppm, there just really is no choice but to switch your chlorine source until it falls back down to a point where you want to increase it again.

At CYA 100ppm, you'll need ~12ppm of Free Chlorine to hold off the algae, and if you use Trichlor to get there and maintain, CYA is just going higher and you'll then have to maintain even higher FC and so on...

On the issue bleach and FC loss due to the sun, the FC from bleach won't go away any faster than any other chlorine source at the same level of CYA. Basically, there is no magic from using a product that mixes Chlorine and CYA. Of course there is the issue of old bleach and available chlorine since it's not stabilized until it gets into your pool. As such just buy 1 month supply of liquid chlorine at a time to maintain freshness.

 

[joecoyle]

Couple things going on here. Your CYA is normally 30-50ppm, but for some reason it's 100 now? What changed? Basically if you believe your CYA is at 50ppm, there just really is no choice but to switch your chlorine source until it falls back down to a point where you want to increase it again.

At CYA 100ppm, you'll need ~12ppm of Free Chlorine to hold off the algae, and if you use Trichlor to get there and maintain, CYA is just going higher and you'll then have to maintain even higher FC and so on...

On the issue bleach and FC loss due to the sun, the FC from bleach won't go away any faster than any other chlorine source at the same level of CYA. Basically, there is no magic from using a product that mixes Chlorine and CYA. Of course there is the issue of old bleach and available chlorine since it's not stabilized until it gets into your pool. As such just buy 1 month supply of liquid chlorine at a time to maintain freshness.

Hiya, this is what changed - i only had dichlor to try and kill off the algae, so basically my FC went from its normal 1-3ppm, I shocked it to 10 using all the cal-hypo i had left. Then ran out of cal-hypo and had to use the only chlorine i had at the time - dichlor - to get it up to 22. Thats what I'm guessing had caused the massive jump in CYA.

I'm now doing a water replacement (60% or so) to get the CYA back to 50 ish, so that I can SLAM and maintain a better FC for a longer period of time. I have literally just received a new batch of cal-hypo yesterday, which i would prefer to use to shock the pool since I'm not overly bothered about CH. If that doesn't work, and after a few days of slamming, i guess I'll invest in some liquid chlorine and try that.

Sound like a plan?

Cheers
Joe

 

[Demegrad9]

Okay, so yeah this makes quite a bit of sense now. If your CYA usually lives at 30-50ppm, then you'll need to maintain high FC than 1-3ppm, more like 6ppm to prevent the original onset of algae which then lead you to use dichlor to kill that.

Maybe the economics of chlorine are different in UK but I'm used to Cal-Hypo being more expensive than Sodium Hypochorite 12.5%. For a vinyl pool, you don't really need the calcium so why pay for it. And the general recommendation I've heard everywhere is calcium should be limited to 350ppm to prevent scaling but I've heard of people having high CH in their city water, so what can they do... So sure it's probably okay to use Cal-Hypo especially since you're replacing so much water, that is if your fill water has low CH. But if you're CH is already in good range, I guess the question is why pay for more?

 

[joecoyle]

Okay, so yeah this makes quite a bit of sense now. If your CYA usually lives at 30-50ppm, then you'll need to maintain high FC than 1-3ppm, more like 6ppm to prevent the original onset of algae which then lead you to use dichlor to kill that.

Maybe the economics of chlorine are different in UK but I'm used to Cal-Hypo being more expensive than Sodium Hypochorite 12.5%. For a vinyl pool, you don't really need the calcium so why pay for it. And the general recommendation I've heard everywhere is calcium should be limited to 350ppm to prevent scaling but I've heard of people having high CH in their city water, so what can they do... So sure it's probably okay to use Cal-Hypo especially since you're replacing so much water, that is if your fill water has low CH. But if you're CH is already in good range, I guess the question is why pay for more?

I suppose I've never really considered the economics of chemistry before - I've always just bought stabilised granules in the form of dichlor and 200g trichlor pucks, and what has always been sold as 'chlorine shock granules' because this is what came in my very first 'startup kit' 11 years ago.

Therefore I've been under the impression that the only way to shock is to use 'shock granules'. Since finding TFP though, i am learning a great deal...

Just checked and the price of 5kg of cal-hypo is £23 and 5 litres of 15% sodium hypochlorite liquid is £10. I can buy 20 litres of liquid for ~£30, but i read that it loses effectiveness over time, so buying in smaller batches may be preferable.

So generally the cal-hypo is more expensive by weight / volume but I think i need to add 4x more liquid to achieve the same dosage according to the instructions - 75g of cal-hypo will raise 10,000 gal by 1ppm versus 400ml of liquid to raise the same 1ppm. So it would seem cal-hypo is better value?? I never was any good at maths (or math if you're in the US )!!

Thanks
Joe

 

[Demegrad9]

Wow, that's funny. Yeah if that's the best prices you can get than Cal-Hypo is about half the cost. I did the same calculation for the prices I get the two products assuming I buy a massive bucket of Cal-Hypo I still get the opposite, basically $0.75 for 12.5% sodium hypo to raise FC 1ppm, and $1.60 to do the same using Cal-Hypo.

 

[needsajet]

Great posts above. You're getting excellent advice.

I'll just add that the liquid will keep for a couple of months quite readily, as long as you don't leave the jug sitting in the sun.

Using your pool size of 26,500 litres, I get 176 ml of 15% chlorinating liquid to raise by 1 ppm FC

I get the following for your pool and calcium hypochlorite to raise it by 1 ppm FC:
48% - 56 g
53% - 50 g
65% - 41 g
73% - 37 g

Glad to hear you're reducing the CYA. And have fun swimming!

 

[joecoyle]

So, my pool is back to its usual crystal clear blue! CYA is down to 50. Much more acceptable! Thank you so much for the advice.

Regarding the numbers for raising the chlorine level - those were what i took off the instructions on the bucket. I'm not sure if the 10,000 gallon figure of 400ml is even close to accurate or whether its US gallons or imperial.

One final question - my FC level has dropped to 12 and since its a really nice day, and half the family are coming over, I'm sure some of the kids will want to swim. Is 12 too high to let them? I don't want itchy eyes etc and parents coming to me kicking off. Normally I would let the FC drop to 3 before letting them in.

Thanks
Joe

 

[needsajet]

12 ppm FC is entirely fine for swimming when CYA is at 50 ppm.

The pool is safe to swim when:

1. The water is clear to the bottom
2. pH is between 7.2 and 7.8
3. FC is between minimum and shock level for your CYA per [FC/CYA][/FC/CYA]

FC at those levels is undetectable, and active chlorine is lower than city tap water because most of the FC is tied up with CYA.

High combined chlorine (CC) can cause discomfort, as well as pH outside the correct range.

Swim lots!!! TFPC is based on keeping the pool open as much as possible.

After the festivities, carry on with a SLAM if need be. Free-floating (planktonic) algae is invisible to the naked eye until it becomes a bloom (green pool) or starts creating colonies on pool surfaces. You can confirm its presence with an Overnight Chlorine Loss Test

 

[joecoyle]

12 ppm FC is entirely fine for swimming when CYA is at 50 ppm.

The pool is safe to swim when:

1. The water is clear to the bottom
2. pH is between 7.2 and 7.8
3. FC is between minimum and shock level for your CYA per [FC/CYA][/FC/CYA]

FC at those levels is undetectable, and active chlorine is lower than city tap water because most of the FC is tied up with CYA.

High combined chlorine (CC) can cause discomfort, as well as pH outside the correct range.

Swim lots!!! TFPC is based on keeping the pool open as much as possible.

After the festivities, carry on with a SLAM if need be. Free-floating (planktonic) algae is invisible to the naked eye until it becomes a bloom (green pool) or starts creating colonies on pool surfaces. You can confirm its presence with an Overnight Chlorine Loss Test

Haha you say swim lots, but Manchester is not known for its sunny days - more like 364 days of rain per year! I'll check the OCLT tonight and see if the FC drops by more than 1ppm.

My pH is 7.2 and CC is 0. I'm always just worried about swimming in anything greater than 3ppm as per the instructions - but i'm learning to trust the TFPC method and science behind it. So with a CYA of 50, i'll maintain a FC of 6 from now on

Although now I'm bothered by all this dichlor and trichlor that I've just bought - i don't want my CYA to rocket sky high again. Normally i just put a couple of trichlor pucks in the dispenser and leave it be.

Should i switch totally to sodium hypochlorite for all chlorine (not just shocking)?

Thanks
Joe

 

[needsajet]

Yes, definitely, stick to chlorinating liquid. You will still get value from the solid stuff. You can use the dichlor and trichlor for raising CYA when needed. Shelf life is very long; just keep it dry.

The trichor is probably tablets or pucks, and those can be very handy in a floater to cover a vacation. Dichlor can be used to recharge your CYA in the spring for the next couple of years. All good

 

[Pool Amateur]

Trichlor and Dichlor last a long time so save it and use it when you need to increase CYA. Cal-Hypo ok as long as CH does not get "too high" trying to find out what that is and how high, especially if it is cheaper than liquid chlorine in your region. Maybe someone will jump in here and tell us what too high is for a vinyl liner and why.

 

[tmurphy]

Can I just say, the information in this thread and the way it has been explained, has been amazing!
I think I am beginning to understand it all
Thank you!

 

[needsajet]

With plenty of rain as you mentioned, you can definitely get away with using more cal-hypo than people with little rain.

You can let you CH level get very high, provided that you're able to keep your calcite saturation index (CSI) below 0.3, at which point scaling becomes possible. The trouble with calcium scaling is that it's hard to remove. You might get away with a CSI up to 0.6, but 0.3 leaves more room for error, and eliminates any risk at all.

More here: Pool School - Calcium Scaling
And for vinyl pool chemical levels, this one: Pool School - Recommended Levels