Oxichlore

[TonyN]

Hi, I returned from holiday (8 days) to a mildly green pool. I did the normal of shocking with Trichlore pastels, 5kg at 6pm. The following morning the algae was worse, and no Free chlorine reading, so I shocked again with 5kg Trichlore pastels, again by the evening the algae was worse and I shocked again with the same dose. Unfortunately the algae was getting progressively worse and no Free chlorine reading.

I was recommended to buy Oxichlore, in liquid form, 5l containers. After putting this product in, bingo! Blue pool again, albeit cloudy.

Now, I cannot get a Free chlorine reading at all. The pool store say this is normal after using this product, and will stay that way for up to two months. And, I should use the slow release chlorine chucks as usual.

I wondered what Oxichlore is, and what is going on chemically.....?

 

[Bama Rambler]

I didn't find a data sheet for it, but it appears to be MPS (non-chlorine shock). It's normally recommended when the CYA is extremely high. It's common to not be able to get a FC reading for a little while after using it.

 

[Donldson]

My guess is that it is sodium percarbonate. It is the base of a product called OxiClean here in the US. It will create hydrogen peroxide, which will act as a chlorine neutralizer. If this is the case you will want to add quite a bit of chlorine quickly (not slowly as the pool store so unhelpfully suggested) to clear it out. Unfortunately if the only 'shock' you have available is trichlor then this is going to really mess up your CYA level. Liquid chlorine or even calcium hypochlorite would be much better options.

Correction: see below.

 

[JoyfulNoise]

It’s not MPS. See this German SDS -

https://www.poolfuchs.de/mediafiles/SDB/05137_Oxischock(DE).pdf

It’s a mixture of dichlor and sodium persulfate. Sodium persulfate is a very powerful oxidizer. In water, this mixture of chlorine and persulfate will kill algae and oxidize contaminants without generating large amounts of combined chlorine. However, the two also react with one another and destroy each other. So, any residual persulfate left in the water will continue to react with free chlorine.

How are you testing your water? For the DPD (pink test), the persulfate will show up as high combines chlorine if you measure CCs.

 

[TonyN]

I'm now very apologetic to admit I use the Mareva test strips and I do normally measure CC's, but annoyingly cannot remember the reading, but only that the FC was zero, non-existant. The link to the german spec. sheet is for granules, but I guess the liquid I used is similar. It will be interesting to see when and how the FC reading appears, unfortunately the Cya is still off the scal at between 150 & 250ppm. I don't want to waste anymore water by emptying the pool somewhat, already done this twice this season, not ideal.

This pool has been a real pain over the last 3 seasons, I'm hoping they will go with the salt system recommendation.

 

[JoyfulNoise]

Well, the problem with test strips is that the FC test can get bleached out by other oxidizers.

Can you get a Taylor test kit in France? LaMotte? You need a DPD-FAS titration test kit to figure out FC and CC with accuracy and confidence. Thevtest kits can get very expensive in Europe but there’s no way to properly manage your pool without one. Your CYA could be A LOT higher than you think and, even with an SWG, you still need to get the CYA lowered. That’s only going to happen through rain/overflow dilution OR water exchange from your municipal supply.

 

[TonyN]

I looked before on the recommendation of TFP for the Taylor 2006 kit, today its 132€ on amazon.fr, very expensive, I think you guys can buy it for around 30 dollars. The Cya has always been high in this pool, I can only put it down to the Trichlore tablets and shock that are readily available here. I was thinking about using non-stabilised tablets and shock when necessary, to try and stop the constant top-up of Cya, very annoying. Maybe if I use 50/50 non-stabilised and Trichlore, the Cya will stop rising throughout the season. Until I can get a chlorine reading, I don't know where I am! Maybe I will ask the client if they would like to invest in the Taylor kit!

 

[JamesW]

Does the label say what the ingredients are?

 

[JoyfulNoise]

I looked before on the recommendation of TFP for the Taylor 2006 kit, today its 132€ on amazon.fr, very expensive, I think you guys can buy it for around 30 dollars. The Cya has always been high in this pool, I can only put it down to the Trichlore tablets and shock that are readily available here. I was thinking about using non-stabilised tablets and shock when necessary, to try and stop the constant top-up of Cya, very annoying. Maybe if I use 50/50 non-stabilised and Trichlore, the Cya will stop rising throughout the season. Until I can get a chlorine reading, I don't know where I am! Maybe I will ask the client if they would like to invest in the Taylor kit!

Every 10ppm FC added by using trichlor adds 6ppm CYA and every 10ppm FC added using dichlor adds 9ppm CYA. So it’s not hard to see how quickly you can build up the stabilizer in the pool within a short period of time.

Do you have access to chlorinating liquid, that is, sodium hypochlorite solution? It’s the same as laundry bleach. That would be the way to chlorinate a pool on a daily basis without adding either calcium or cyanuric acid to the water. But it does require testing to know how much and how regularly to add it.

And, just for information, a Taylor K-2006 is about $70USD for the kit with the 0.75oz reagent bottles (or ~$100 for the commercial grade kit with larger reagents).