Bags of shock-how much CYA boost?

[Rob621]

Took the cover off this weekend to find algae growing on the floors and walls. First time I haven't opened a clear pool since we had it installed. Oh well, guess it was bound to happen. I actually think the growth may be from last year after closing. The water is pretty clear, I can easily see to the bottom of the pool and samples are clear. Water temp is around 50-54 degrees so algae shouldn't be growing.

Now for the question. Checked CYA and I'm at about 20 (maybe a little less). Based on this my shock level is only about 10. I am going to initially hit it with bags of shock rather than a bunch of bleach. I'm thinking the bags of shock will boost the CYA to a more appropriate level while hammering the algae. Does anyone have any idea on average how much of a CYA boost I can expect to see?

Thanks,
Rob

 

[woohoo]

Without full test results we cannot help determine the answer to your question of how much CYA will be added. Use the pool calculator and enter your current numbers and then use the Effects of Adding Chemicals at the bottom of the pool calculator page to help determine how much CYA will be added. I would be more inclined to add bleach now as you can do it with a low FC level based on the low CYA you have in the pool. Then add the CYA later using other methods. Before shocking, you might want to get PH in line depending on your current readings. Good luck!

 

[Bama Rambler]

If you're using Dichlor then 4 lbs will raise your FC by 11 and your CYA by 10. So 4 bags is all you should add until you've completed the shock process. Unless you have the Dichlor lying around, I would use bleach to shock the pool.

 

[Rob621]

Thanks for the responses thus far. Bama - I agree with your calculations, that's what I come up with. You say you would use bleach though. Let me clarify, I follow the BBB method and normally only use bleach to chlorinate. However, in this particular case the shock seems to make more sense. At $3.50 a bag (x4) versus $3.00 a jug (x4) for Wally world bleach the shock bags end up costing me $2.00 more total. With this approach I get the added CYA which I need (since I am low at 20). From then on out, bleach all the way. Otherwise I need to purchase stabalizer to bring the CYA up. From a cost perspective, the shock bags seem to be the way to go in this instance. Am I missing something or some negative affect?

 

[jblizzle]

Your approach generally makes sense if you had a clear pool. But since you are in the shocking process, raising CYA now means you must maintain higher shock FC levels which could result in more expense.

If you completed your shock process and then measured that your CYA was low, you could then dose with di- or trichlor to maintain your normal FC levels while adding the needed CYA.

 

[DeadAquaRite]

Your approach generally makes sense if you had a clear pool. But since you are in the shocking process, raising CYA now means you must maintain higher shock FC levels which could result in more expense.

If you completed your shock process and then measured that your CYA was low, you could then dose with di- or trichlor to maintain your normal FC levels while adding the needed CYA.

Thanks for this response, and the earlier help. My thought process was exactly the same as the OP. I had read several times that elevated CYA = elevated shock shock levels. However, it didn't really register that raising CYA while shocking was counterproductive until they asked and you replied.

I know answering newbie posts can get tiring (and repetitive), but I really do appreciate you taking the time to answer. I'm digesting as much as I can, but until you learn and gain first hand experience, sometimes it takes a more direct approach before things "click".

Thank You!

 

[Leebo]

You could always go 1/2 instead for shocking. This will take your CYA levels up to 30.....The shock levels will go from 10FC for a CYA level of 10 up to a 13FC for a CYA level of 30. Only a small increase, but the extra stabilizer in your pool will help keep the chlorine in. Shocking with a CYA level of 10 is a PITA as I've found out as I've tried it for the last week or so. It's just not worth the extra headache knowing the most of the chlorine you're pouring in is going up in the air.

In this case......go for the bags of shock. You seem to have a good grasp on what you're adding and the side effects of each product. Sometimes however those side effects can be helpful too.

ps....I got the same numbers as Bama and you did.

 

[jblizzle]

Shocking with a CYA level of 10 is a PITA as I've found out as I've tried it for the last week or so. It's just not worth the extra headache knowing the most of the chlorine you're pouring in is going up in the air.

I agree that it seems better to have your CYA on the order of 20-30ppm for the shocking process to protect it from the sun.

Although there are special cases where CYA at 0 is probably fine at the start (like a SWAMP or a Baq conversion), where the FC is being used almost immediately by the organics before the sun gets to it. However, once everything is dead and the water starts to clear, you are probably better off getting up to the 20-30ppm to finish off the shock process.