Why do we not use shock?

[Propbndr]

You will need to keep an eye on your calcium and pH levels so you don't develop scale.

Agreed, right now my CH is 100, ph is 7.2. Experience has shown me that 2 of the “logs” last a week and raise my CH by 50. My repaired SWG will arrive and be installed Tuesday. The extra calcium will actually help me get closer to a 0 CSI and LSI.

 

[pooldv]

Yes! At TFP we know what it is, what it does, how to test for it and how to adjust accordingly.

 

[mknauss]

In the past those 'logs' or 'pucks' of compressed cal-hypo were reported to leave a goo behind that was the binder. What was your experience Prop?

 

[JimMarshall]

I use everything and have no problems as long as I keep the CYA in check. I’ll shock once a month with dichlor or cal-hypo granules, use trichlor tabs in an inline chlorinator and occasionally use liquid chlorine instead of tabs when the CYA starts to creep up. I just use test strips. No problems so far ((fingers crossed)). If you are good figuring out the chemistry, you’ll know what to do to keep that water clear. I like the convenience of tabs bc I can’t spend every day adding liquid chlorine, I don’t have that kind of time and no pool service. But just using tabs forever will definitely raise the CYA too much and cause problems. You need to take a break from trichlor.

It takes ~2 minutes to test and add LC. And you don’t even have to do it daily once you know your pool.

 

[Propbndr]

In the past those 'logs' or 'pucks' of compressed cal-hypo were reported to leave a goo behind that was the binder. What was your experience Prop?

I was doing a SLAM. So I have only fully used 2 and just put in my second pair. No goo in the skimmers so far. My experience so far is that they maintain a fairly constant FC level.

 

[CrisVH]

It takes ~2 minutes to test and add LC. And you don’t even have to do it daily once you know your pool.

Yes, I know. What I was saying is that you can use anything you want as long as you know what you’re doing. You don’t need to exclusively use LC. I’ve used a combo of both LC and trichlor tabs with much success bc I know what works for my pool. And the water is clean and clear. And btw, I learned about using LC on this forum and it has been a huge help. But I don’t use it exclusively and it works for me. 4 years of pool ownership and counting. Lots of trial and error at the beginning but now I think I’m doing pretty good, better than the “pool guys” that want to charge me $60 a visit.

 

[frustratedpoolmom]

I'm not so optimistic about it. Rather I see it as another way to get money out of people. First they sell trichlor which raises the CYA. Then they sell algaecide to mask the overstabilization problem. Then they sell these, which raises the CH. Then they sell the scale inhibitor. Then, when they have nothing left to sell, they can tell the customer that their TDS is just too high and it is time to drain and start over. Probably sell some fresh sand or a new cartridge for their filter to go with that water change as well.

They charge you for the cure to the disease they sold you...

Well said!!!

In the past those 'logs' or 'pucks' of compressed cal-hypo were reported to leave a goo behind that was the binder.

I had a client that had purchased a large amount of them before I came on the scene, they had a plaster pool, their CH was low, so we agreed to use them (and I discounted their fee) for the season. I did not experience any goo, but they were in the skimmers and not a floater or inline chlorinator.

But man, they are PRICEY!!!

 

[sccm_sysadmin]

I made some graphs to help explain. They're not perfect representations of what happens in real life (yes CYA slowly decays and decreases if you replace water, FC levels jump up and down as the pool is used or algae breakouts occur, etc), but these charts should give you a good idea of the potential issues with using the "pool store once-weekly shocking method".

First graph: Standard pool-store recommended shocking. Assumptions:

• 120 days
• CYA starting at 40ppm.
• Each bag raises FC by 10ppm and CYA by 6ppm.
• Shocking once/week.
• FC dropping by 3ppm per day due to UV exposure.
• When CYA hits 100ppm, the pool store says to start adding 2 bags of shock, because 1 bag isn't working anymore!
• Note how FC drops to 0 and stays there for several days until the pool is shocked again.
• Any values where FC is less than 7.5% of CYA (ie: less than the "minimum" FC level) is highlighted in green to represent the possibility of algae growth.

Second graph: TFP methods. Assumptions:

• 120 days
• CYA starting at 40ppm.
• FC dropping by 3ppm per day due to UV exposure.
• FC wavers between 4ppm and 7ppm every other day when you dump in some bleach. Note that with a SWCG or a Stenner pump for automated dosing, this graph of FC over time will be closer to a straight line.
• Note the lack of possibility of algae growth since you're keeping the FC above the minimum levels at all times, AND your CYA levels are not rising.

Third graph: example of exponential population growth. You might be able to get away with the pool store once-weekly shocking method for awhile, but eventually exponents catch up. If you don't keep the FC levels high enough for long enough to kill all the algae, those that survive will keep reproducing (even if you can't see it with your eyes!), and start using your FC even quicker than shown in the graph. One day your pool looks a little cloudy, maybe you're too busy to drop in some more shock, then the next day it "just turned green for no reason!!", because the growth rate of the algae finally went asymptotic. Then the pool store tells you to use 2 or 3 bags of shock, and the process starts over again.

 

[laprjns]

first graph: Standard pool-store recommended shocking. Assumptions:

• 120 days
• cya starting at 40ppm.
• each bag raises fc by 10ppm and cya by 6ppm.
• shocking once/week.
• fc dropping by 3ppm per day due to uv exposure.
• when cya hits 100ppm, the pool store says to start adding 2 bags of shock, because 1 bag isn't working anymore!
• note how fc drops to 0 and stays there for several days until the pool is shocked again.
• any values where fc is less than 7.5% of cya (ie: Less than the "minimum" fc level) is highlighted in green to represent the possibility of algae growth.

You forgot daily dosing of both FC and CYA with the used of pucks which would change the results significantly.

 

[sccm_sysadmin]

You forgot daily dosing of both FC and CYA with the used of pucks which would change the results significantly.

Then the entire graph would be green.

On a more serious note, I actually left that out on purpose to show just how quickly you can start to have issues purely from shocking weekly. It would definitely be worse if I added in the effects from using daily dosing with pucks.