Problem at pool opening

chumpy36 · Postby **chumpy36** » Mon 09 May, 2011 16:46

Opened the pool to find a terrible algae bloom....

I used algaecide and shock to get the water a good bit clearer (pale green) but after that good start I seem to have stalled...

Water is very cloudy and pale green
I can't seem to keep chlorine in the pool (even after shock it goes down to 2ppm very quickly)
Total Alkalinity is very high at 260
I've tried clarifier in case the algae particles were too small for my sand filter
I've shocked repeatedly
PH was a bit high but after using PH down it is now normal at 7.2
Water foams a lot when shock is added.
At a loss.... any ideas?

thanks

Postby **chem geek** » Mon 09 May, 2011 19:45

You aren't using nearly enough chlorine. I hope you are using chlorinating liquid or bleach. Did you test your Cyanuric Acid (CYA) and Calcium Hardness (CH) level? If the CYA is high, then the Free Chlorine (FC) level you need to kill the algae will be higher. Read Defeating Algae where you will note that shocking is not just a one-time process, but adding chlorine frequently to MAINTAIN a high enough FC/CYA ratio.

If the water then turns cloudy and does not clear in a few days running the filter 24/7, then you can also read Add DE to a Sand Filter to improve filtration.

chumpy36 · Postby **chumpy36** » Mon 09 May, 2011 21:08

chem geek wrote:You aren't using nearly enough chlorine. I hope you are using chlorinating liquid or bleach. Did you test your Cyanuric Acid (CYA) and Calcium Hardness (CH) level? If the CYA is high, then the Free Chlorine (FC) level you need to kill the algae will be higher. Read Defeating Algae where you will note that shocking is not just a one-time process, but adding chlorine frequently to MAINTAIN a high enough FC/CYA ratio.

If the water then turns cloudy and does not clear in a few days running the filter 24/7, then you can also read Add DE to a Sand Filter to improve filtration.

I am not using liquid chlorine but rather dichlor granulated shock... I assume you think bleach is better?

My test kit does not do calcium hardness or CYA. I've got a Taylor K-2006 on the way though. I could get the water test at pool store tomorrow. I will post when I have that. I guess I could go get a shit-tonne of bleach at walsmart at the same time...

So if one gal does 5ppm per 10k gallons, I assume you would want 9 total gallons for a 30k gal pool? That should get it to 15ppm? I guess I really need to buy more than 9 gal I guess to keep the levels up?

Thanks for your reply...

J

chumpy36 · Postby **chumpy36** » Tue 10 May, 2011 13:53

Ok, got the water tested...

Fac 3.0
tac 4.0
calcium hardness 190
cya 25 (they say too low)
ta 200
ph 7.4
copper 0
iron 0
tds 850
phosphates 1000

Postby **chem geek** » Tue 10 May, 2011 17:03

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. So if your CYA was initially 0, then using Dichlor was OK to get some CYA into the water, but at this point you want to kill of the algae so I wouldn't use too much more Dichlor -- not more than about 10 ppm FC worth. Then use chlorinating liquid or 6% unscented bleach and raise the FC level to at least 12 ppm and keep it there by adding it multiple times per day if necessary. Run the filter 24/7. The pool should get clearer each day. Please read the links I gave that give more detailed info and please get your own good test kit, either the Taylor K-2006 or the TFTestkits TF-100.

chumpy36 · Postby **chumpy36** » Tue 10 May, 2011 21:18

chem geek wrote:For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. So if your CYA was initially 0, then using Dichlor was OK to get some CYA into the water, but at this point you want to kill of the algae so I wouldn't use too much more Dichlor -- not more than about 10 ppm FC worth. Then use chlorinating liquid or 6% unscented bleach and raise the FC level to at least 12 ppm and keep it there by adding it multiple times per day if necessary. Run the filter 24/7. The pool should get clearer each day. Please read the links I gave that give more detailed info and please get your own good test kit, either the Taylor K-2006 or the TFTestkits TF-100.

I applied 10 gallons of bleach tonight after sundown...

Chlorine level went off the chart of my test kit which has a high of about 5ppm. I tested again at 10 pm and it had gone down significantly. I would guess something like 7ppm?

Apply more of the bleach tonight? I have ten gallons left. I also have plenty of dichlor? Why would using the dichlor be an issue getting rid of the algae?

Thanks again

Postby **chem geek** » Tue 10 May, 2011 21:41

Dichlor becomes an issue if you use too much because the CYA added by Dichlor doesn't go away so it builds up. CYA significantly lowers the active chlorine level which is roughly proportional to the FC/CYA ratio. If you double the amount of CYA in the water, then if you don't change the FC level you cut the active chlorine (hypochorous acid) concentration in half. This lower chlorine concentration kills algae more slowly and eventually it can get to the point where algae can grow faster than chlorine can kill it.

In fact, this is what happens in many pools that use Trichlor pucks/tabs all season if they do not have significant water dilution or have pools poor in algae nutrients or use supplemental algaecides. For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm so even at a low 1.5 ppm FC per day chlorine usage, Trichlor will increase CYA by 1.5*30*0.61 = 27 ppm PER MONTH so by the end of the season one can get algae growth which at first may not be visible and looks like unusually high chlorine demand.

So add more chlorine to get it up again. The fact that it is getting used up means it is killing and oxidizing the algae. You will be done with this shocking when the pool is clear, your overnight FC drop is < 1 ppm, and your CC is <= 0.5 ppm (if using a 10 ml sample size in the FAS-DPD test).