Chlorine Generation

[B69CA]

Hello Folks...

I hope this post finds everyone well and enjoying summer...

I've done extensive reading on this forum (amazing) and I think I know what is going to be said but nonetheless I don't want to bait anyone's response and was hoping for a little help.

I have a SWG (Pool Pilot Dig-220) with a RC35/22 cell. The cell is around 1 - 1.5 years old and the Dig-220 was replaced only last year. We use (and thus heat) our pool all year (have 2 little ones) and right now its at 86 degrees, which is pretty much what I keep it on.

Typically, the maintenance on my pool is minimal. A cup of acid every week or so, a bag of salt every so often and the usual stabilizer etc... In the 4 years I've owned the house / pool I've had a single bout of algae which went away fairly quickly and was down to the cell packing up...

Anyway - the other day I noticed some yellow algae on the sides of the pool, not much but I wanted to get ahead of it. I took a sample to the pool shop and they read a chlorine level of 1PPM and low salt.

So...

I added a bag of salt, a packet of stop yellow and 1 jug of chlorine yesterday afternoon.

I took another sample back this morning and my chlorine was 0PPM, salt was 3000. I didn't want to add chlorine as I wanted to make sure my system was working so when I got back I put the system on boost.

Took another sample around 4PM and TC:1ppm C:1ppm CC:0ppm pH:7.6 TA:115ppm CH:295ppm Stab:60 ppm - salt is 3000ppm

The guys suggested that the system being on boost should have generated more...

Here is my issue though.

I'm seeing 19v with 6.5A from my cell and I do see bubbles coming out of the vents when the generator is on (don't see any when generator is off but pump is still running).

The yellow algae has gone but I'm concerned that my system is not generating chlorine.

Pool is 10'000 gallons.

I also did my own drop tests this afternoon and I got chlorine at around 1.5ppm - 2ppm, a little higher than the pool shop and in the "ideal" range according to my drop tests - and I did 2 separate tests with 2 separate kits and 2 sets of reagents.

Hence why I'm additional concerned / confused.

Does anyone have any thoughts / suggestions?

Many Thanks,
Jon

 

[msgtdan]

Welcome

From reading you probably know we're not big on pool store tests. If they're accurate then the algae is eating up the chlorine as fast as the SWG can produce it. It is hard to shock with the SWG even with boost. Use liquid chlorine to bring it up to shock level and maintain. But to know your shock level we need to know your CYA level, and that's about the worst one the stores do. You really need your own test kit.

 

[jblizzle]

Welcome to TFP!!!

You have not been maintaining a high enough FC level, it should never be below 3ppm with the high CYA levels in a SWG pool.

Your FC got too low, algae started and is now consuming the FC faster than the SWG can make it.

Read Pool School. Get one of the recommended test kits. Perform the shock process using bleach.

Is that what you were expecting?

 

[B69CA]

In fairness I usually keep my chlorine at 5ppm, mainly due to the fact that the kids use it pretty much every day. Its held pretty stable running my generator at 65% or so hence this little dip caught me off guard - my bad for not being more vigilant...

Thanks folks - yes exactly what I was expecting. What I didn't want (and didn't get) were suggestions to check x and y on my SWG as regardless of the shops reaction, I don't believe I have a problem there and I know enough to figure that out.

I've always done my own tests in addition to the pool shops and they've always been within range in fairness but granted I have typically used the wallmart type kits.

Will order the kit recommended in the school tonight so I have it on hand.

I'll check my levels tomorrow but between now and the kit arriving is there anything I can do to help remedy my situation or at least move it in the right direction?

Thanks again folks, much appreciated help...

Regards,
Jon

 

[jblizzle]

You can just turn the SWG off make sure the pH is in the low 7s and start adding bleach up toward the shock level of 24ppm (assuming the CYA of 60ppm is correct).

 

[B69CA]

Thanks again Jason.

I will order a kit tonight so I can get the CYA myself accurately but assuming that 60ppm as per my report is correct, when you say add bleach, you do mean liquid chlorine?

And (sorry for the continued questions) when you say shock to 24PPM, what measurement is that as my chlorine is usually at a 5 and 24 seems considerably higher hence I think i'm using the wrong number.

I will be reading the school later when I get home from work so more than likely my answer will be in there so apologies for the RTFM question...

Many thanks (again)

Jon

 

[jblizzle]

bleach = liquid chlorine ... literally the same thing only different concentrations. I use the 8.25% Walmart brand bleach from the laundry aisle although now found that the 10% "liquid chlorine" in the pool area is actually a little cheaper in terms of $/ppm. Some pool stores sell 12% in refillable containers that can end up even cheaper.

And by 24ppm, I mean the free chlorine (FC) level. Yes, your test only goes to 5ppm, that is why you need the FAS-DPD chlorine test.

 

[JasonLion]

You should also note that stop yellow consumes massive amounts of chlorine. Once you have added it, which I don't recommend, you must follow their directions for adding dramatic amounts of chlorine on a schedule as directed. No SWG can ever keep up with that demand and if you don't add chlorine manually to keep up you will have an extended period of low FC levels which will just let the algae get started again.

Yes, bleach and liquid chlorine are exactly the same thing, though often sold at slightly different concentrations.

When you are fighting algae you need to use dramatically higher FC levels than you would normally use. Once the algae is established in the pool, normal chlorine levels will only slow the algae down a little, not eliminate it. The higher your CYA level, the more chlorine you need to use. I suggest you take a look at the how to shock your pool directions in Pool School.

 

[B69CA]

Thanks Guys, already learned a massive amount - very helpful...

I do need a better test kit - will sort later...

One final question, if I shock the pool to 24PPM how long will it usually take (I expect there a loads of variables but rough estimates) before it comes back down, or more to the point, before the little-ones can swim again?

Thanks again,
Jon

 

[jblizzle]

You should pass the 3 criteria in the shock process before you let the FC drop below the shock level (this may take days). Once you pass, the kids can swim when the FC is below the shock FC level based on your CYA.

pool-school/shocking_your_pool

 

[B69CA]

Hi Guys,

Just wanted to come back and give an update to this...

I ordered and received the TF-100 kit and did a complete analysis of my numbers. Firstly, wow, what a difference a complete test kit does and I certainly see the difference in accuracy with my tests than those of the pool shop.

Anyway, first couple of chlorine tests proceeded to show that I had combined chlorine of around 1 - 1.5ppm - this remained over a few days. I brought my CYA to 70 and shocked my pool to 22ppm - slightly lower that the number in the recommendation but not by much. I initially shocked the pool using liquid chlorine (10%) from Wallmart and then kept it around 20ppm with the SWG running at 80%.

After 2 days my combined chlorine was zero and my overnight loss was zero. The pool also looked remarkably better, almost better than I've seen it for a while.

I've spent a few days keeping my pH low so that I can bring down my alkalinity to the recommend levels in pool school - I'm getting there with that. My TA reading is around 110ppm right now and coming down by around 10ppm each day. I'm having to add 1 cup of acid each day to keep the pH between 7.0 - 7.2 so nothing major.

My chlorine is still quite high due to it being quite cloudy right now hence the sun isn't hitting it much - as an example my SWG has been off all day today and my chlorine has dropped from 20ppm to 17.5ppm. I don't want to use chemicals to drop it so I'm hoping we see the sun again soon. My CYA is around 70 so no doubt that's protecting too.

So all in all, my SWG is working perfectly and my chlorine problem was most likely down to something organic eating it up as suggested here in the TFP forums. I'm glad I took the advice, bought the kit and didn't replace my cell as suggested by the pool shop.

Current Levels:
FC - 17.5ppm
CC - 0ppm
TC - 17.5ppm
pH - 7.2
CYA - 70ppm
TA - 110ppm
CH - 360ppm
Salt - 3500ppm
Temp - 90f

Thanks again guys for all your help.

Regards,
Jon

 

[JasonLion]

 

[msgtdan]

Glad it work out for you. And now you're in control!

 

[ping]

Stop adding acid to correct the pH while the FC is above 10 ppm. The pH should read high due to the raised FC and is not considered to be accurate if the FC is above 10 ppm. The pH is normally adjusted to 7.2 before adding chlorine for the shock process and is ignored until the FC drops below 10 ppm.

 

[B69CA]

Ah OK - I missed that one...

I'll stop adding acid at this point then - hoping my FC levels come down over the next couple of days as I really don't want to chemically reduce them if possible.

Thanks again,
Jon

 

[jblizzle]

No need to chemically reduce the FC ... it is safe to swim when the FC is less than shock value if that is your concern ... although the pH is now a bit questionable and could be a little low.

 

[B69CA]

I'll take another pH reading tomorrow and see where I'm at. If its still a concern I guess I could add a little Borax as per the school recommendation? I took a measurement this afternoon and it was reading 7.5 so it is showing an increase hence it might just be worth leaving over the next couple of days???

What do you experts think? I'm more concerned about pool damage than swimmers right now, the weather is rainy so the pool is not really being used that much.

 

[JasonLion]

There is no reason to expect chemical damage to the pool from your FC levels. That isn't really a possibility until well above mustard algae shock level.

 

[B69CA]

Thanks Jason,

I was more thinking about the pH... If my pH is now too low is there a chance that the water will be acidic and cause damage?

Thanks again!
Jon

 

[duraleigh]

Leave your pH alone for now. If low, it is not dangerously low. Let your FC get below 10 ppm and then test to get reassurance.