How long should a shock process take?

[stev32k]

This is only the second time I've had to shock the pool and it's taking much longer than the first time. I'm now on day 12 and the pool is still greenish. Before starting the test results were:
FC 5.5
TC 0
pH 7.4
TA 50
CYA 20

Before starting I cleaned out all the leaves and debris and back washed the filter. There was a ton of pine tree pollen on the surface and even more oak tree pollen on the bottom. Next I added 1L of HCL to bring the pH down to 7.2 and enough 6% chlorine to to get 13 ppm which is what the chlorine/CYA chart said was needed for a mustard algae shock.

When I started the pool was a very pretty forest green color. After two days it turned to a distinctly yellowish-green. After three days it was a greenish white and I raised my chlorine target to 20 ppm. It is still a greenish-white on day 12. The pump has been running 24/7 since starting and I've had to back wash 3 times.

One big difference I've seen is that chlorine consumption is much lower this time around than it was the first time. The last time I used 60 gallons of 6% bleach in 6 days and the pool was clear. Now after 12 days I've only used 53 gallons of 6% and the pool is still greenish. The target level of 20 ppm is the same I used last time when the starting CYA number was 40. I've been watching the over night CL loss and it rarely gets over 1.5 ppm. Also I have not detected any combined chlorine and last time the CC jumped up to 2 - 3 ppm after the first day.

Is this normal or could something else be going on?

 

[duraleigh]

Hi, Steve,

That's the 64k question and the unfortunate answer is "as long as it takes"

I know it is frustrating to read reports of a pool going crystal clear in just a day or two when yours is taking so long. I wish we knew a definitive answer.

I can reassure you there is nothing else going on, if that helps.

There have been a few folks here on the forum that have resorted to a floc treatment........most with no results but some report overnight clearing.

As a rule, that is normally something we would not suggest but that call is yours.....it might work.

PS - All your test results and procedures look absolutely correct to me....I don't see any errors.

 

[JohnT]

I suspect you are losing a lot of your chlorine during the day because of your low CYA. It normally won't take anywhere close to as long as you are running, but weird situations do arise. I opened my pool to dark green last Wednesday, and 10 182oz jugs of 6% and 10lbs of trichlor was all it took to get to where I could return to normal chlorination.

 

[duraleigh]

JohnT's sharp eyes caught the CYA I overlooked. 20ppm is VERY difficult to measure so you may be less. You will want to up it anyway when you finish the process so I would suggest at least 30ppm...perhaps 40.

 

[stev32k]

OK, I added enough CYA to take the level up to about 35 ppm. Also put in 6 pucks. Now I guess I just wait and watch.

 

[stev32k]

Now on day 14 the pool is greener that it was two days ago. It is also more cloudy. The day before yesterday I could make out the bottom drain this morning it can't be seen and the color has gone from greenish-white to completely green. On Monday I added enough CYA to bring the level to 35 ppm and raised the chlorine target from 20 to 30. Yesterday I raised the level again to 40 ppm. At 7:00 last night the CL was 42.5 ppm. This morning before sunrise at 6:00 AM the level was 42. Now at 9:30 AM the chlorine level is still 42 and the CC is 0.

I believe the testing chemicals are good because the results match closely to what they should be when I add bleach. One 182 oz jug of 6% chlorox will raise the chlorine level in my pool by about 2.5 ppm. I've measured that many times and it is pretty constant (2.4 - 2.7) depending on the water level.

I've had the polaris running about 8 hours per day and the main pump running 24/7. The pressure drop across the filter has only increased by 3 psi in the last five days and I expected it to increase by about 3 or 4 psi per day.

Is there anything else I should or should not be doing?

 

[Bama Rambler]

Have you inpsected the sand filter for channeling?
I'd also suggest manually vacuuming as that gets the stuff directly to the filter faster.
You might have some metals if it gets greener the more chlorine you add.

 

[stev32k]

I thought about opening the filter and will do that if it quits raining today. The only metal (that I know of) in the pool or pumps and piping is the ladder in the deep end and the light fixture and both are 316 SS. I don't believe there is copper or mild steel anywhere in the system.

I'll keep the polaris off to let any solids settle and then vacuum to the filter and see if that helps clear it up.

I don't understand why there seems to be little to almost no chlorine consumption overnight or why I'm not seeing any CC. I would expect to see significant overnight chlorine loss and an increase in combined chlorine.

Is there any risk to running the FC as high as 40+ and can (or should) it go higher?

 

[Bama Rambler]

Can you post a pic of your water?
And a full set of test results including CH?

I wouldn't go much above the recommended shock level for your CYA in a vinyl pool. You can bleach the liner.

 

[stev32k]

Here are three shots - Monday, Tuesday, and today just a few minutes ago.

The last test results this morning were:

FC 42
CC 0
TA 50
CYA 35

I don't test for CH and chlorine is too high to read pH, but before I started the shock it was 7.2

 

[Bama Rambler]

I'd do a CH test to be sure it's not high.

I'd also take a sample to a local pool store and have them test for metals.

Other than that, keep shocking.

 

[chem geek]

Don't forget that you can Add DE to a Sand Filter to improve filtration.

 

[stev32k]

Don't forget that you can Add DE to a Sand Filter to improve filtration.

Yes, I know I've done that in the past and will again when the turbidity gets lower. Now I doubt I could run for an hour before having to backwash. At least that's what happened last time I added DE when the water was very turbid. :?

 

[stev32k]

Just an update. On Saturday I opened the filter to see what I could see and found the sand level to be about 5" below normal. I had added sand last year and it was gone then some. I've known I washed some sand out when back washing, but had no idea it was that much.

I've known for some time that the pump (1-1/2H.P) was over sized for the filter and I had installed a valve on the outlet of the filter to throttle the flow. What was happening was the back wash flow was too high for the filter and the valve on the discharge side did not help. The result was the loss of a lot of sand and likely channeling in the filter due to the low sand level.

I re-piped the pump discharge piping (not a single leak or drip on the first try ) and installed a valve and pressure gauge to be able to throttle the flow when filtering and back washing. When I throttle the valve to give the discharge pressure that corresponds to the max filter flow (if the pump curves are close) there is a 17 psi drop across the valve. Previously the inlet pressure to the filter was 27 psi. After the changes the inlet pressure is 10 psi. I've now back washed twice and can't see any sand in the back wash water.

The pool shows a definite improvement in clarity. It's not clear by any means, but for the first time in weeks I can see the bottom drain without straining. It is also getting less green - still has a green cast, but it's getting better.