Can anyone confirm this CYA problem ?

[DaveOB]

I would appreciate if someone could please confirm if my thinking here is correct, before I go and dump all the water out the pool on Monday.

Specs :
36,000 liters.
Outdoors.
In-Ground.
Fiberglass Lined ( 3 years old ).
Outside the pool ( in the following order ) :
Speck 0,75 kW pump.
2 bag sand filter.
Cartridge filter.
T-Piece split - 1 to the pool return inlet, other to a 7 coil solar system, and that to a second return inlet. Each inlet gets about equal flow.
Pool temperature 22 Celcius.
Currently end of winter, but summer water gets to 30 celcius.

Problems started about 2 months ago ( mid winter, air temp around 24 celcius day, 16 celcius night ). Green algae on the walls. Vacuum would not suck it off, but brushing would easily remove it.

Added chlorine granules to shock, but no effect. Pool store sold me Algae remover liquid ( TWICE ) and that worked great, with a clear pool within 36 hours.

Week later, same problem. And the chlorine level is very high ( test strips ).

So research here has me thinking that the CYA level is too high, so the chlorine, although high, is being held captive by the stabiliser ( CYA ) and not enough active chlorine to kill the algae ( if I am allowed to use the term : chlorine block ? ).

Local pool shops don't have the liquid test kits. Found a pool shop in the city and went there this morning.

Readings are :
TDS ( Total Disolved solids ) 500 ( Ideal < 1500 )
Stabilizer 100 ( ideal 40 - 80 )
Total C + F 5 ( ideal 1.5 - 3 )
Free 5 ( ideal 1.5 - 3 )
pH 7.8 ( ideal 7.2 - 7.6 )
Acid 1
T.A. 125 ( ideal 120 - 150 )
C.H. ( Calcium Hardness ) 220 ( ideal 175 - 225 )
Copper 0 ( ideal 0 )
Iron 0 ( ideal 0 )
Mang 0 ( ideal 0 )

I was told that the Stabiliser 100 reading should be 40 to 80, so not too high.

However, having done some reading online, I thought to ask what the maximum CYA reading was on the test - guess what - 100.

So next asked them to repeat the stabiliser test, with 50% pool water, and 50% tap water. Reading was still 100.

Next was 25% pool water and 75% tab water - result : 70 -- so 70 x 4 = 280 CYA !!

I think this explains why my high Chlorine has little effect on the water / algae.

If my research is correct, the only solution is to drain more than 85% of the water and refill.

I think if this is correct, I might as well drain all the water and start with a 'clean slate'.

Would appreciate if anyone could point out something obvious that I have missed, and / or any advice or special treatments that should be done to the empty pool before the refill.

Regards
Dave

 

[duraleigh]

Yes, your CYA is astronomically too high. Drain/refill is about your only option to manage your pool successfully.

Once you have CYA down around 40-50, you need to understand how your CYA got that high and take steps to prevent repeating the problem in the future.

 

[DaveOB]

Thanks for the reply.

A while back the pool shop 'experts' had me add stabilizer and change from ( HTH ) Calcium Hypochlorite ( I think unstabilised ) to (Waterwell Ultra-chlor ) Sodium Dichloroiscyanurate.

My understanding is that the Dichlor adds 9 ppm CYA for every 10 ppm FC, but as the FC is burnt off, the CYA simply accumulates.

 

[duraleigh]

My understanding is that the Dichlor adds 9 ppm CYA for every 10 ppm FC, but as the FC is burnt off, the CYA simply accumulates.

That's correct. Dichlor has to be used VERY carefully in pool water management.

 

[DaveOB]

My understanding is that the Dichlor adds 9 ppm CYA for every 10 ppm FC, but as the FC is burnt off, the CYA simply accumulates.

That's correct. Dichlor has to be used VERY carefully in pool water management.

Yes, this is a small snippet of info that I think the 'expert' left out - I wonder why ?

I can't think of any time in my life that I have given deliberate misleading or inacurate or incomplete advice with the goal of profiting from it in any way. But then I guess that's why I can sleep well at night.

 

[Butterfly]

Welcome to the forum

Be aware of the water level in your area before you drain. Most folks do a partial drain/refill dance.

Depending on your fill water CH, if you want, you can use cal-hypo until your CH reaches the recommended levels of 220-320. Then stop using cal-hypo. Too much CH is not a good thing and the remedy is the same as for too high CYA, water replacement. pool-school/recommended_levels

It would help if you add your pool/equipment specs in your sig and your location in your profile.

Do you have a pic of your pool for us? :-D

 

[chem geek]

My understanding is that the Dichlor adds 9 ppm CYA for every 10 ppm FC, but as the FC is burnt off, the CYA simply accumulates.

That's correct. Dichlor has to be used VERY carefully in pool water management.

Yes, this is a small snippet of info that I think the 'expert' left out - I wonder why ?

I can't think of any time in my life that I have given deliberate misleading or inacurate or incomplete advice with the goal of profiting from it in any way. But then I guess that's why I can sleep well at night.

Welcome to the pool industry -- barely one step up from the dietary supplement industry in its level of integrity. It isn't always the fault of those working in the pool stores since they often just pass on what they are told by the manufacturers and their reps. For the manufacturers to tell the truth about how quickly CYA increases from stabilized chlorine or CH from Cal-Hypo would not be in their best interests. In fact, some stabilized chlorine manufacturers have gone further claiming that "only FC matters, CYA doesn't matter" where they ignore CYA's effect on reducing chlorine's effectiveness for disinfection, oxidation and algae prevention.

If you think this is bad, just wait until a pool store employee claims that their Alkalinity Up is different and better because it contains "sodium hydrogen carbonate" instead of the baking soda you can get at a grocery store that contains "sodium bicarbonate". These are both synonyms for the same chemical. And then there are the complete falsehoods that are ridiculous, but that is borne from ignorance and poor training of temporary employees hired quickly for the summer months. See this post for more equivalents of pool chemicals.

 

[DaveOB]

OK. So I have taken the 'plunge' and drained and refilled the pool.

And a special thanks to everyone on the forum for all the info I have learnt over the last few days.

Now I am not too sure about the next step.

I can not get the expert test kits ( in South Africa ) that are so well recommended on the site, so have to work with the test strips and HTH 4 in 1 liquid kit.

I have added HTH ( cal-hypo 63% ) and raised the FC to 4.2

pH 7.2
TA 40 - 60 ( 40 liquid test, 60 test strip ) so am assuming around 50
Calcium hardness 1.5 ( based on pool calculator info about adding the cal-hypo ) so will be adding some calcium chloride flakes to raise that a bit.
CYA 0

Next added 2kg sodium bicarb and expect pH of 7.47 and TA 82

Now I want to bring the CYA level up to a minimum of 30.
Stabiliser info says add 1kg cyanuric acid, but that would drop the pH by 0.5, making pH = 6.97

So how do I increase the pH again ?
The packaging on the pool stores 'pH Increase' says not to be used on fiberglass pools, but to use 'Alkalinity increase'.
But 2kg 'Alkalinity increase' will increase TA by 32 and pH only by 0.07 - so to get the pH up to 7.4 will need 12kg of bi-carb, and will increase the TA by 192, making TA = 274 which is way too high.

Is borax safe to use in a fiberglass pool to raise the pH after adding the stabiliser, or is there a better solution ?

Regards to all
Dave

 

[Bama Rambler]

Borax is completely safe to use in a fiberglass pool.

Are you using the Pool Calc to figure how much chems to add?

 

[DaveOB]

Hi Dave J.

Yes. I am using http://www.thepoolcalculator.com/

The only reason I asked the question was after I saw the warning on the packaging in the pool shop about not using soda ash in a fiberglass pool, and didn't seem to find any info regarding borax in fiberglass pools.

Having read a bit more, it looks like airation can also be used effectively to increase pH, and if so I don't need to go spending money on borax, or Alkalinity Up ( followed by acid and airation to drop the TA and increase the pH )

Since I have 2 inlets in the pool ( 1 direct from the filter, and 1 from the solar coils ) I can easily add a pvc pipe to one of them to make a mini fountain ( the kids are going to love this idea ) and the other inlet will easily manage any additional pressure that this could put on the plumbing. The ball valves that I have for the 2nd inlet can be opened a bit more and used to control the pressure to the fountain.

 

[Bama Rambler]

Any of the chems recommended here can be safely used on any pool surface. Follow the recommendations on how to introduce it to the pool and you'll be fine.

 

[linen]

Having read a bit more, it looks like airation can also be used effectively to increase pH, and if so I don't need to go spending money on borax, or Alkalinity Up ( followed by acid and airation to drop the TA and increase the pH )

Since your TA is low, I wouldn't use areation, I would use soda ash or borax. Afaik, there is no problem using soda ash in a fiberglass pool...many folks on here have.

By the way, trust the drop test for TA.

 

[DaveOB]

Thanks for the advice all.

Given that the source of the current 'challenge' is the addition of the CYA, which is going to drop the pH, does the following logic have merit ? ...

I read that the CYA is going to take a few days to fully dissolve and become effective ( or something along those lines ).

So my thinking is to add another 2kg of bi-carb in the morning, lifting the TA from 72 to 104, and the pH from 7.47 ( before addition of stabilizer ) to 7.54.
Then watch the readings daily while the CYA kicks in and drops the pH, and then gradually add the borax ( around 800g ) to keep the pH at target 7.4.

Result should be pH 7.39 and TA 110.

Is my logic flawed ?

 

[linen]

Did I miss something? I thought your TA was 40?

 

[DaveOB]

Did I miss something? I thought your TA was 40?

Hi linen

I did mention earlier that I had " Next added 2kg sodium bicarb and expect pH of 7.47 and TA 82 "

I was later advised to rather use the liquid test result for TA ( 40 instead of either the 60 reading on the test strip or the avearge of 50 that I had chosen ) so the addition of the 2kg bi-carb this morning should have increased to TA 72.

Another 2kg bi-carb tomorrow morning should increase TA to 104.

Regards
Dave

 

[linen]

Make sure you confirm the TA. If you TA is up around 72, I would not purposefully raise if further now (our recommendation is 70-90 ppm, unless you will be using trichlor or dichlor to chlorinate). Just keep an eye on your ph, and if it drops below 7.2, raise it back up with Borax.

 

[heythatguy]

Being that I work in the sales and service industry I do find the bad rap given a bit misleading and almost offensive. The one trick in regards to CYA levels, probably being extremely high because somebody floated way way too many tablets. Just because your floater will hold 12 is not a reason to put 12 in it. We tell customers 3 tabs, and to check that weekly, during the spring and summer, along with liquid chlorine. We tell them in the winter to pull the floater out and to not float tablets, and use liquid chlorine weekly.

 

[jblizzle]

Being that I work in the sales and service industry I do find the bad rap given a bit misleading and almost offensive. The one trick in regards to CYA levels, probably being extremely high because somebody floated way way too many tablets. Just because your floater will hold 12 is not a reason to put 12 in it. We tell customers 3 tabs, and to check that weekly, during the spring and summer, along with liquid chlorine. We tell them in the winter to pull the floater out and to not float tablets, and use liquid chlorine weekly.

Then you are going to have a bad time on this forum

How is that a CYA trick. Is that 3 pucks for a 5k pool or a 30k pool? What was the starting CYA level? Are you saying you test the CYA weekly? Do you recommended higher FC levels as the CYA rises? {I do not actually expect a reply to any of these questions}

If you just set the CYA at the beginning of the season and stick the liquid chlorine, then there is no need for the pucks or to be testing the CYA often. Sure some people with short swim seasons that do large drains in the winter can be fine using pucks all season ... ASSUMING, they actually monitor the CYA and adjust FC accordingly.

 

[chem geek]

Being that I work in the sales and service industry I do find the bad rap given a bit misleading and almost offensive.

It is not misleading nor offensive -- it's a chemical fact. For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. If the daily chlorine demand is 2 ppm FC per day, then that is an increase in CYA of 36 ppm per month. As the CYA climbs, if the FC is not proportionately raised then algae can grow faster than chlorine can kill it.

In my own pool 10 years ago, I used Trichlor pucks in a floating dispenser and because of my electric mostly opaque safety cover over my 16,000 gallon outdoor pool my chlorine demand was 0.7 ppm per day (the pool was kept warm at 88ºF as it was used for therapy, but only once or twice a week). After one and a half years, the water started to turn dull and then cloudy and I couldn't keep up with the chlorine demand -- an algae bloom was starting.

This is no surprise because of the rise in CYA that started at 30 ppm but after 11 months of pool use rose by 0.7*30*11*0.61 = 141 ppm so would be 171 ppm, though I actually measured 150 ppm because CYA does slowly degrade from chlorine and there was a little splash-out and carry-out. I had an oversized cartridge filter so no backwashing, only cleaning once a year, and I had a pool cover pump that put the water into the sewer and not in the pool. So there was minimal water dilution.

The only reason I didn't get algae in the first year was that I was using an algaecide, though every other week instead of every week. The FC target was 3 ppm and I was at risk of getting algae when the CYA rose significantly above 40 ppm.

Sure, you can point to pools with high CYA and no algae and no one is saying that CYA causes algae, because it doesn't. CYA significantly moderates chlorine's strength (known chemistry since at least 1974) and that's a good thing to have in moderation but a bad thing when overdone. You can certainly manage a pool at higher cost by using phosphate removers or algaecides or weekly shocking or other techniques to keep algae at bay in spite of too low an FC/CYA ratio, but what we promote on this forum is FC/CYA management so that these extra products or techniques are not needed.

Our local pool store that services over 2000 residential swimming pool targets 4.5 ppm FC and they dilute the water when the CYA gets to 100 ppm. They shock the pool if it is dull or looks like algae is forming and if that doesn't work they use a phosphate remover. This hybrid approach works for them, but they really didn't understand why they needed to target a higher FC, but they just knew they needed to do that to have most of their pools not have problems using Trichlor. If they tried to manage their pools at 3 ppm FC, they would have many more problem pools every season and cost a lot more to manage them with phosphate removers or algaecides.

After my experience during my first couple of years of pool ownership, I learned pool water chemistry and learned from The PoolForum (thank you, Ben Powell) and since then I have not had to use algaecide, phosphate remover, clarifier, flocculant, enzymes nor do any regular shocking. The pool is now used almost every day so the chlorine demand now averages 1 ppm FC per day. The 12.5% chlorinating liquid and acid I get from my local pool store costs me around $18 per month. Realistically, for those without mostly opaque pool covers the costs would be higher at around $35 per month but that's still pretty inexpensive and the pool is trouble free and has been for the last 8 years and I anticipate will be until the day I die.

 

[heythatguy]

Being that I work in the sales and service industry I do find the bad rap given a bit misleading and almost offensive. The one trick in regards to CYA levels, probably being extremely high because somebody floated way way too many tablets. Just because your floater will hold 12 is not a reason to put 12 in it. We tell customers 3 tabs, and to check that weekly, during the spring and summer, along with liquid chlorine. We tell them in the winter to pull the floater out and to not float tablets, and use liquid chlorine weekly.

Then you are going to have a bad time on this forum

How is that a CYA trick. Is that 3 pucks for a 5k pool or a 30k pool? What was the starting CYA level? Are you saying you test the CYA weekly? Do you recommended higher FC levels as the CYA rises? {I do not actually expect a reply to any of these questions}

If you just set the CYA at the beginning of the season and stick the liquid chlorine, then there is no need for the pucks or to be testing the CYA often. Sure some people with short swim seasons that do large drains in the winter can be fine using pucks all season ... ASSUMING, they actually monitor the CYA and adjust FC accordingly.

Sorry if I used the word "trick" when it wasn't actually a trick. Nothing like being attacked on a forum for typing a thought. I do not know the size of the pools when a customer comes in, nor do I know the CYA level, and I doubt the customer does. If a customer brings water in to me I will gladly test it weekly, bi-weekly. Most customers add a gallon of liquid chlorine to the pool a week. Again I do not know the sizes of the pool. So there levels could vary big time.