Using Stabilized Chlorine to Shock Treat a Pool

[SantiSuk]

In an unusually long five weeks away from Thailand my pool 'got away' from pool boy (brother-in-law), who managed to measure and keep salt levels high enough to generate required amounts of chlorine, but ignored my pleas to let me know if the chlorine levels nonetheless got low.

So I returned to find very low chlorine levels, a snowy white layer in the pool, pH levels unmeasurably high and TA at 140. One week of shock treatment, painstakingly slow floor vacuuming, backflushing and 20 litres of acid has restored some balance and crystal clear waters. But the combined chlorine level is still a little high at 0.4ppm (TC of 1.5) and my pool, having finally got back down to 7.2pH seems to be crying out to be fed with more acid on a daily basis.

So that's why I thought I would check out the internet to double check the quantities of chlorine I should add to get a more effective shock treatment. I came across a reasonably learned article by a US state health board that included the guidance:

Stabilized chlorine compounds, such as DICHLOR or TRICHLOR may not be used for “shocking” because the permitted level of cyanuric acid would be exceeded over the season. It also would cause the water to have elevated chlorine levels for days.

I recognise the danger of the first (and indeed it was extensively covered in a recent thread here) but I don't find that a problem for me as hitherto I have not found it necessary to shock the pool very often - ie combined chlorine has generally stayed around 0.2ppm. However the second statement caught my eye. Does anyone else avoid using stabilised chlorine for shocking because it does not burn-off quickly enough? Does the fact that highish chlorine levels will hang around for a few days (which they do) mean that I can never hope of getting a perfect shock?

All of the chlorine I have previously bought in Thailand advertised as being quick acting and for shocking does have stabiliser in it!

[curtklay]

It's the cyanuric acid in stabilized chlorine that can cause problems if the level gets too high. You should be able to find sodium hypochlorite (liquid) or calcium hypochlorite (granular) at any pool store. Neither contain stabilizer and are the standard for shocking with chlorine. If the water is clear, you can also use non-chlorine shock (potassium monopersulfate) commonly called "oxidizer" that will release combined chlorine without raising the chlorine level too high to swim.

Edited November 12, 2014 by curtklay

[SantiSuk]

Thanks Curtklay. I'm not so sure about the ease of access to those products - I reckon you must live in Pattaya or Phuket. If the former, can you let me know which shop does stock it. Thepprasit?]. I may have to accelerate my visit to Bangkok and do a side trip to Pats.

I have two pool shops within 250k of my place in Lower Issaan - both in Meuang Ubon (JD Pools and Joyeaux Pools) and neither of which would stock anything other than a few basics when it comes to range of chlorination/sanitation - I checked out their chemical ranges a year ago. Swimming Pools Thailand is an excellent online store but they don't cover non-chlorine shock-stuff. Pool Doctor's website doesn't currently click thru' to Chemicals products.

[curtklay]

I live way up north in Phrae, so I know it can be difficult to find the right products here. My advice on chemicals comes from my prior life in the US, where I worked in the business for many years. I'm not familiar with pool stores in Pattaya or Bangkok, but would guess that there are larger stores that carry a good line of shocking products. The trick is finding them. Online shopping could be the best route. I'd give Pool Doctors a call since their website isn't working. With 2 stores (Bangkok and Pattaya) I would think they would have a full range of chemicals.

[Anthony5]

In 5 weeks time your salt levels went that low that not enough chlorine was generated anymore and that you needed 20 liter of HCI to get your pH back to 7.2 ?

Is your pool 500.000 Gallons big or do you have actually no idea about pool chemistry.

Please don't answer, i've read through your numerous other threads in this forum about the constant issues you have with your pool.

[SantiSuk]

Nasty posting.

If it was a response to my posting on another subject, the objectionable part of which I apologised to you for, then I understand - but you owe me a sorry too!

[Anthony5]

Nasty posting.

If it was a response to my posting on another subject, the objectionable part of which I apologised to you for, then I understand - but you owe me a sorry too!

I owe you an apology if you explain your ridiculous figures.

I have never seen a pool lose so much salt in 5 weeks that it doesn't chlorinate anymore, unless maybe if there are heavy thunderstorms 24 hours a day for 5 weeks, and even then.

My pool which is always filled close too the edge, so will overflow as soon as it rains, needs salt added every 6 months during the raining season, before it gets below the required levels.

Adding 20 liter of HCI to a 100.000 litew pool, which is a pretty large pool by the way, would lower pH by 6.15 and TA by 100, but in a 60.000 liter pool which is more common it would lower pH by 10.25.

Do you want to say that your ph was in the range of +15?

To give you a comparison. Chlorine has a pH of around 12

Edited December 7, 2014 by Anthony5

[SantiSuk]

I may have dome JD Pools a disservice in post #3 when I said that they did not stock shock chlorine that is non-stabilised. I was passing their depot/shop in Ubon a couple of weeks ago and called in to check. The shock chlorine that the sales girls showed me made no mention of stabilisation so I'm going to assume it is non-stabilised and give it a whirl (since no-one was around who could give any information one way or the other). 899 baht for 5kg of 25g tablets

The pack instructions are fairly unhelpful as to dosing (see if you can make anything definitive of it from the photo), so I will have to do my own calculations by monitoring the effect of a small dose and working out a regular maintenance dose (what it takes to raise TCL from 1.0ppm to 2.0 for instance). I should also be able to confirm whether it is stabilised or not by how quickly the level fades.

One question - does chlorine tend to have a linear relationship between weight and impact? In other words if I can establish how many grams it takes to raise TCL by 1ppm, can I assume it takes 10 times that quantity to raise TCL by 10ppm?