Milky water turning darker after shockings

[fillmypool]

Problem: The pool was green with algea. I shocked it and the water turned milky light green. I shocked again and the water went almost white. Then slowly it turned again darker a bit. I shocked for third time and now every day the water goes darker til now it is brown.

FC: 7
TC: 7
pH: 7.3
TA: 100
CH: 200
CYA: >150

My pool: 20k gallons inground
Pool chemicals: chlorine dichlor, polyquard algicide
My pump & filter: 2hp with hi-rate sand filter
Other info: none I can think of

Thank you
Marty

[chem geek]

You should not be using Dichlor (or Trichlor, for that matter) because your CYA is already too high at >150 ppm. Some stores sell Dichlor powder for shocking and that is totally irresponsible. The following are chemical facts independent of concentration:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

For shocking, you should use unstabilized chlorine such as chlorinating liquid or bleach (or if your CH is low you can use Cal-Hypo).

You should have done several partial drain/refill to lower the CYA level and remove some of the algae. With your high CYA level, it will take a lot higher FC level to clear the pool. Since you have to lower the CYA anyway, that's why doing a partial drain/refill is better to be done first. See this post on how to get rid of algae. You can see this thread for how a pool can be cleared using chlorine alone, but not at a high CYA level such as yours.

You have other choices to kill the algae and clear the pool more quickly, but they are more expensive and have side effects (e.g. copper algaecide, flocculant) and they won't fix your CYA problem. Filtration with backwashing is also key.

It's also possible that in addition to algae you had iron in the pool and the higher shock levels with high FC oxidized the iron making the water look brown. Though a metal sequestrant could be used, the partial drain/refill to reduce the CYA level will reduce the iron level as well unless your fill water is high in metal content.

Richard

[fillmypool]

I read what they said at that link you gave. It didn't talk about the cyanuric acid.

Once the algae is dead it will often turn gray or even milky white. It can still take the filter up to a week to clean the water from this point. You should see a visible improvement in the water each day. If you don't see a daily improvement, the algae might not all really be dead, or there might be a problem with your filter.

From what you write here (so knowledgably) I figure the start of my problems was in the wrong chlorine. I read abot the cyanuric acid here before and wondered about it. I'm going to drain the pool and I figure roughly half the water should do it. Then after I can use cal hypo and then liquids for chlorine.

I have not a big hurry to clear the water but I don't like looking at the color like it is now. The sooner I fix it up, the happier I will be. I must have it perfect for the coming spring weather.

Thanks Richard
Marty

[chem geek]

I read what they said at that link you gave. It didn't talk about the cyanuric acid.

Marty,

The link did talk about CYA:

Second, the FC level you need to target depends on the cyanuric acid (CYA) level. The higher the CYA level the more FC it is going to take. If you don't have any idea of your CYA level, you risk either not using enough chlorine, and failing to get rid of the algae, or using too much chlorine, and causing metal corrosion and shortening the life of your vinyl liner (if you have one). If your CYA level is too low, most of your chlorine will be lost to sunlight, instead of fighting algae. If your CYA level is too high, you will need huge amounts of chlorine, which rapidly becomes impractical.

and it gave a link to a more detailed post here where it says the following:

It is also important that the CYA level not be too high. If CYA is too high cleaning up the pool will take really huge amounts of chlorine and quickly becomes impractical. If a reliable test shows that your CYA level is above 90 you should replace water to bring the CYA level down to 90 or lower before continuing.

If you are going to drain/refill (i.e. "replace water"), be careful about that since you shouldn't drain too low if you have a high water table or have an above-ground pool. Multiple partial drain/refill or a continuous drain/refill are other approaches. You could also use the sheet or silage bag method where you drain underneath the sheet or outside the bag while simultaneously filling above the sheet or inside the bag. The sheet drops and you then remove it when it gets to the bottom. That uses less water than multiple drain/refill.

Richard

[fillmypool]

I checked with the local pool guys and they said there are no issues with the water table in our area. My neighbor confirms this. So I have started draining and will dump a half the water in one shot.

Thanks for all the help and guidance Richard. I'll keep you posted with my progress.

Marty

[fillmypool]

I finished the draining. Whew

I put both my hoses in the pool and it's starting to fill as we speak. I got a couple of gallons of chlorinating liquid and I'm ready to go!

[chem geek]

Since you drained nearly all of your pool water, you'll want to add calcium chloride to raise the Calcium Hardness (CH) unless your CH is very high in the fill water. You'll also want to add some Cyanuric Acid (CYA) so that the chlorine will be protected from the UV in sunlight, assuming the pool is exposed to direct sunlight. Obviously, you'll not want to go too heavy on the CYA. You can either add it via pure CYA which takes a while to dissolve or you can use Dichlor initially as your source of chlorine until the CYA gets to where you want it to be. There is also a faster dissolving liquid CYA product, Instant Pool Water Conditioner, but it's about twice as expensive as pure CYA.

Richard

[fillmypool]

My pool is full now. I poured one gal chlorine and the pump is running. The clean fresh water made the pool look better already.

I'll let the pool run, clean it and then test the water again. I can give more feedback in a day or two.

Thank you again for your valuable help

Marty

[fillmypool]

OK, nearly one week has gone by and my pool looks much healthier. I had my water tested and here we go:

FC: 2.0
TC: 2.0
pH: 7.2
TA: 110
CH: 180
CYA: 65

I am happy with how the water is right now. Did I do alright?

I read here about a bb method and I'm going to give that a try. I need to get some 20 mule team borax and I have the chlorinating liquid. I still have some dry acid so I think I can start this weekend.

Thanks for all the help and support

Marty

[chem geek]

With a CYA of 65 you should have the Free Chlorine (FC) not get any lower than about 5 ppm. 2 ppm is asking for trouble, specifically algae growth. You could be lucky since you just refilled and perhaps your fill water doesn't have phosphates in it, but to prevent algae growth you should have a minimum FC that is around 7.5% of your CYA for a manually dosed chlorine pool. If you really want to have a lower FC level, then you should use a weekly algaecide (PolyQuat 60) or a phosphate remover, but if you just maintain the correct FC level relative to CYA you won't need these extra products (at extra cost).

To raise the pH, just aerate the water by turning your return jets upwards and leaving any cover off. Your TA is already high enough so by aeration you'll raise the pH with no change in TA. It's true that using Borax will raise the pH without as much rise in TA as with pH Up product (half as much rise, actually), but aeration won't make the TA rise at all.

As for your Calcium Hardness (CH), I don't believe you said what kind of pool you have. If it's vinyl, then your CH is fine. If it's plaster/gunite or fiberglass or has exposed tile with grout, then you'll want the CH higher and can use The Pool Calculator to help figure that out.

Please read the articles at the Pool School as they will help you in maintaining your pool.

Richard

[fillmypool]

Update: I have switched to chlorinating liquid and added the borax.

My pool looks good and the levels are now holding steady with me adding chemicals twice a week.

Thank you to everyone for the help and special thank you to chem geek

[fillmypool]

Update: all is great and I am relaxed and happy .

I continue to visit here and read on the forums and I hope I have no worries in the hot summertime.

Marty

[chem geek]

Marty,

Glad everything worked out for you. Have fun swimming this summer!

Richard