After algae clear, when do I stop shock

[TRHOD12]

First off, praise to this site. I've recently purchased a house with an pool, and had ABSOLUTELY no idea what to do with a pool (other than jump in and swim).

This past weekend we had a weekend long get together with a huge swimmer load for 3 days. I had been maintaining my chemistry, but wasn't prepared for the sudden increase swimmer load combined with rapid increase in sunlight and temp.On wednesday I got the dreaded green hue to the water. Not bad, but noticable to me. The water did not cloud up, but was starting to get green.

Well, I've been following the forums advice for killing the algae. And it has worked. I've been maintaining my chlorine at 15-20ppm (dropped to 11-13ppm once or twice), testing chlorine three times daily, brushing twice daily, followed by vaccum and then backwash filter.

Well, after a day and a half the water is clear and no green hue again, which is good. Tells me I'm on the right path. The one concern I'm having is that today from the 2pm chlorine test to the 7:30pm chlorine test I was STILL loosing 5ppm of chlorine. This is telling me that I probably am still battling algae.

My question is, when do I stop maintaining the 15-20ppm shock level and let the pool chlorine level reduce to a normal usable level??? Do I stop shocking since the water is clear and not green, or do I go by what my chemistry seems to be telling (that the algae is still eating the chlorine) and I need to maintain the shock level till the chlorine level does not drop 5ppm in a 5 hour time period. Or can I assume that the 5ppm drop is due to having a higher chlorine content and increase exposure to sun (cover has been off since I started shocking) causing a faster chlorine burnoff?

Thanks for all your assistance.

Chemistry
FC= shock 15-20
CC= 0
TC=shock 15-20
alk= 120
pH=7.8 (was mantained at 7.5 before the shock started)
CYA= 50
temp=78

24K inground pool, hayward sand filter

Another question about the pH. My pH had been very stable at 7.4-7.6. Once I started the shock wednesday nite the pH jumped to 7.8 and had been holding there. I added 4oz of muratic acid tonight, but haven't tested the pH since adding. Should I have left the pH alone?? Will it come down on it's own after the shock is over??

Blessings,
TRHOD

[aylad]

If your chlorine consumption is still higher now than it was before your pool went green, then keep the shock level up until the consumption slows down. Usually if you have a CC of zero and the water has become clear, you're safe, but it won't hurt to keep it up another day.

As far as pH goes, it won't come down after the shock level drops, unless you've gotten false high readings due to the elevated chlorine levels. In any case, 4 oz shouldn't hurt anything.

Janet

[TRHOD12]

Janet,

Thanks for the response.

Well, good news. When I went home this morning and test the CL level it was maintained at 17ppm. That tells me the algae is all dead.

My pH had held steady at 7.8 after adding the 4 oz muratic acid, so this morning I added 100ml (that was all I had left in the bottle). When I tested the pH this afternoon the pH is now 7.6.

A side note to the pH thing. When I started the shock and I also notice the pH had jumped from 7.5 to 7.8, I notice a large brownish orange stain had appeared on the bottom of the liner infront of the return jet. I was getting concerned, and started reading and found that the increased pH could cause metal stains to show up. Well, what I notice when the pH went back down to 7.6, the stain is now gone. Again, Praises to the forum for helping me out with this.


We jumped in the pool tonight before I had to head to work. It was AWESOME. I'll do my best to make sure I don't get in this predicament again.


Blessings,
TRHOD

[waterbear]

Sounds like your jump in pH was actually a false reading caused by the high chlorine levels. When you shock to high levels you should not try and ajust the pH. It is really not possible with a liquid reagent test. Wait for the chlorine to drop to below about 10 ppm and if the pH is still high adjust it then.

[TRHOD12]

Would the shock also make my CYA level read high??
I had the CYA level checked at the local pool 2 weeks ago, and checked it with the 234 kit earlier this week and the level was 30.

edit--Today when I looked at it, it appeared to be 50.

I guess the take home message when shocking is not to look at the other chemistry?? Would that be a safe assumption??

Blessings,

[waterbear]

Would the shock also make my CYA level read high??
I had the CYA level checked at the local pool 2 weeks ago, and checked it with the 234 kit earlier this week and the level was 30.

I guess the take home message when shocking is not to look at the other chemistry?? Would that be a safe assumption??

Blessings,

Well, high chloinen levels will interfere with both pH and TA tests but they should have minimal effect, if any, on CYA and calcium hardness. However, IMHO, you should not try and balance the water while the chlorine is at shock levels.
The CYA test is somewhat subjective and it is quite possible that the pool store did not give you an accurate reading. Keep tabs on it yourself and see how it goes.