Noob with a problem

[Alaskaman]

Hi guys, I'm in a bit of a jam and would appreciate your help.
I just got a maintenance gig at a local hotel, and this is the problem...
When I took over I had a total of about 15 min training on a pool/spa setup, and
pool school isnt for a few weeks yet.
Last week we had a huge body count... between 50-100 bodies per day on Sat/Sun, followed by at least 25 a day since. The ORP levels bounced up to 900, and I tried to shock it and got my butt kicked.

So I drained 19,000 gallons to start fresh Mon Morning.....but I still don't know diddly. I know the incoming water will be 40 degrees, Ph= 8.4 and I think the CC on arrival will be 3-4ppm. (from last weeks spa draining)

How do I fix it ASAP to get it opened back up???

BACKGROUND: 19,000 gal plaster in ground pool. Large sand filter I'd estimate 45 gal or so?? 2In inlet. Large pump(maybe intelliflo), drained it in 4-1/2 hours. Watermatic C-660 ORP/Ph controller, and we use 12% hypochlorite liquid as well as muriatic acid through the controller.

The guy I took over for said he never shocked the pool, but would on occasion throw a couble of tabs (84%) into the skimmers. I assume I should plan this differently??


Any help or advice would be great, I'll check the forum from work & see what it looks then (if its done filling yet)

Thanks guys,
Larry

 

[chem geek]

Welcome to TFP!

If the pool is properly maintained with sufficient levels of chlorine, then you shouldn't need to shock the pool much at all. I presume you "got [your] butt kicked" because you shocked the pool so the chlorine level was too high for re-entry, is that correct? Was the FC higher than 10 ppm? In most states, re-entry is allowed below an FC of 10 ppm. I'm not sure why you drained just because you shocked the pool -- you could have just added some dechlorinator (thiosulfate or other reducing agent) to reduce the chlorine levels. On the other hand, with such high bather loads, some water replacement is needed anyway.

I don't understand why you tried to shock the pool when you noticed the ORP was high. A high ORP doesn't mean that shocking is needed -- it means the active chlorine (or other interfering oxidizer such as non-chlorine shock) is high. That's a bit strange unless the ORP first went down with the high bather load and then the automatic dosing of sodium hypochlorite went overboard. 900 mV is extraordinarily high so I suspect that the unit has not been calibrated properly and it probably has a high setpoint (can you tell me the setpoint -- that is, the ORP level that the controller tries to maintain?).

I presume this pool is outdoors, but is it exposed to direct sunlight? If so, was there any Cyanuric Acid (CYA) aka stabilizer or conditioner in the water?

For the fill water, do you believe the CC will be 3-4 ppm because monochloramine is used by your water district? That's pretty high for monochloramine which is usually closer to 1-2 ppm with 3 ppm being a maximum.

Trichlor tabs are usually close to 90% available chlorine; I'm not sure what the "84%" tabs are that you are talking about. I don't think adding tabs in the skimmer is the thing to do when there is unusually high demand. Trichlor tabs take too long to dissolve and they also increase the CYA level. If for some reason your controller is unable to respond quickly enough, you can manually add more chlorinating liquid to the pool, but I'd be surprised if the controller can't keep up even with a high bather load unless the controller's "max" flow setting isn't very high.

As for fixing up the pool quickly, do a test now on the fill water with a good test kit such as the ones we describe here. Since you are using a hypochlorite source of chlorine and since I presume you want to minimize the amount of acid addition, that means you'll want to keep the Total Alkalinity (TA) on the lower side so start out with 80 ppm to see how that goes -- add baking soda if it's too low.

I presume you'll want some, but not too much, Cyanuric Acid (CYA) in the pool water to protect the chlorine from breakdown from sunlight and to somewhat moderate chlorine's strength. I wouldn't go higher than 30 ppm for CYA since this is a commercial/public pool and you want higher sanitiation/oxidation rates. In fact, with the high bather loads you are describing, you might want to just use 20 ppm CYA and your FC target would be on the higher side so around 20% of the CYA level -- that means 4 ppm FC with 20 ppm CYA. There won't be any CYA in your fill water so you'll need to add it to the pool. CYA is very slow to dissolve so you can add it to a sock to hang over a return or put it in a T-shirt in the skimmer IF you have alternate suction flows to the pump such as floor drains. The 4 ppm FC with 20 ppm CYA corresponds roughly to an ORP of 675 mV on an Oakton sensor or 710 mV on a Chemtrol sensor, but you would just dose with chlorine to measure a 4 ppm FC and then set the setpoint on the controller with whatever it is currently measuring.

Of course, get some chlorine into the water as soon as you can, especially as it starts to warm up -- you can manually add some chlorinating liquid to it if you aren't yet circulating and having the automated controller set up yet.

Adjust the pH using acid to lower it -- or perhaps your automated controller will do that for you.

You'll probably want your Calcium Hardness (CH) to be around 300 ppm to protect the plaster surfaces. There will be some, but not very much, CH in your fill water so you'll likely need to add more using calcium chloride. Have the pH closer to 7.5 before you increase the CH or else you can get cloudiness.

Richard

 

[anonapersona]

Are you in Alaska? (looking at your name)

Indoor pools are much differnt than outdoor pools, so let us know that ASAP.

 

[Alaskaman]

Yes, I am in Alaska, and yes it is Indoor.
I tested the fill water & it is about as anticipated. while testing the Ch, a prob I'm having is that it reads 5ppm, I add the reagent and it still says 5ppm....is my reagent bad?? it hasn't frozen, and is only 6mo old.

As to chem geek's question, I shocked because the water was burning the eyes, and was very Ch smelling.. I determined this was chloramine, and everything I could find said to shock it.
I'm still not sure if I didn't get enough in to shock it or too much. I added 3 gal 12% the first time, 3more gal 12 hrs later... I let it sit for 24 hrs and it never settled. The Ch test (even diluted) instantly went hot pink bordering on purple, and I took this as way too much CC.
Since I couldn't solve it, I went with the almost guarantee, which was to empty it. I am currently aerating while filling hoping to lower it

I do not know if the utility uses chlorine or chloramine but I will find out & let you know.
I appreciate your help, I'm kinda lost on this one.

Larry

 

[Alaskaman]

Oh, I almost forgot...We do not have any thiosulfate, but I am trying to source some locally.

 

[PaulR]

I tested the fill water & it is about as anticipated. while testing the Ch, a prob I'm having is that it reads 5ppm, I add the reagent and it still says 5ppm....is my reagent bad?? it hasn't frozen, and is only 6mo old.

From the description I am assuming this is a DPD test. It sounds like you're not fully understanding how the test works:
1) You put in some drops, it turns some shade of pink, and you compare to color blocks to get a reading.
2) You put in some other drops, and do the comparison again.
The first reading is FC, the second reading is TC. CC = TC - FC. So, if the last set of drops doesn't change the color, then your CC = 0 which is a good thing.

Oh, I almost forgot...We do not have any thiosulfate, but I am trying to source some locally.

Not sure I follow this--you shocked, then completely drained and refilled, and now you're shocking again? If you are able to maintain the pool reasonably, you probably won't need to shock (or not often) and thus won't have any need for thiosulfate (or hydrogen peroxide, which will also do the job, and might be easier to find).

Other questions still waiting for an answer: What's the ORP setting on the automation? What exactly is the ingredient list on these 84% tabs?

If you give us more details, we'll be able to do a better job of helping with whatever questions you have.
--paulr

 

[frustratedpoolmom]

Just to clarify things - we use FC, CC and TC for referencing chlorine. CH is almost always used to reference Calcium Hardness....just so there is no confusion.

I can tell you off the bat you are going to need an FAS-DPD test kit that can measure FC and CC up to 50ppm, it doesn't sound like your kit can differentiate between total chlorine and combined chloramines....and it only goes up to 5 so that won't really help you.

oh I see Paul answered you - I missed that. Sorry if I'm repeating anything.

Aerating only raises PH under certain conditions. It's not going to "lower" anything...are you trying to lower PH or the chlorine level?

So if your PH is high right now you need Muratic Acid to lower it. Once you can determine CC vs. Free Chlorine you can determine how to proceed with shocking. Once you have a better chlorine test, you'll KNOW if you are shocking high enough instead of guessing.

I would recommend that in the future with such high bather loads the water be monitored more frequently and if necessary close the water for an hour to adjust the chlorine levels. I don't know anything about ORP controllers so I'll just be quiet about that but I'm pretty certain you don't want to solely rely on it, when the bather load it that high, especially if it was already a problem.

Good luck, we're here to help in anyway we can.

 

[chem geek]

Thanks for the update of information. Yes, it does sound like the very high bather load overwhelmed the pool. The controller might not have been able to keep up so too much monochloramine built up OR the controller did keep up and overshot and had the chlorine get too high causing more irritating nitrogen trichloride to be produced -- the latter is more consistent with the high ORP reading.

It's possible that what was most needed was a good maintenance level of chlorine and a good airing out of the room -- oxidizing bather waste takes time, especially in indoor pools. If this pool is going to have such high bather loads regularly, then some form of oxidizer assistance may be needed -- something like ozone or even UV to take care of the chloramines. Some try using non-chlorine shock (MPS), but to be most effective it needs to be added before the bather load and some find it to be irritating.

As others have mentioned, you really should get a FAS-DPD chlorine test. Also, since this is an indoor pool, but as a commercial/public pool, your state may not allow any CYA in the pool so I'm not going to recommend even the small 20 ppm amount I normally would. It would likely have reduced the irritating nitrogen trichloride smell, but would have combined chlorine (CC) as monochloramine take longer to oxidize (and urea would take longer to oxidize as well).

 

[PaulR]

Also, since this is an indoor pool, but as a commercial/public pool, your state may not allow any CYA in the pool so I'm not going to recommend even the small 20 ppm amount I normally would. It would likely have reduced the irritating nitrogen trichloride smell, but would have combined chlorine (CC) as monochloramine take longer to oxidize (and urea would take longer to oxidize as well).

That's a good point, state laws & regs differ. I happened to be at a public pool here in N.Cal recently, and got a chance to peek at the posted regs--required minimum CYA 20, and 100 is cause to close the pool. But we know some other states forbid CYA entirely. Hopefully there is some paperwork at your job that will tell you what's required.
--paulr

 

[Alaskaman]

Ok, I reopened it today, the refill took, but my CH is only 60ppm so I am trying to raise that. Paul, sorry about Ch vs CH, I didnt realize until reading more the use of CH. BTW, is there a 'BBB' way of raising hardness?
I still don't quite understand why it took off, but I will def be asking you guys for more help along the way.
I am unsure of how much bather load the Auto-controller can handle, should I get in the habit of loading tabs into the skimmers prior to the weekend? The pool is not monitored over the weekend, maybe we will have to revamp schedule to have a chem add on weekends if necessary?
The state allows CYA but I don't have any, I thought it was naturally occurring until reading more. This is used as a stabilizer??? And how much do I need?
Anyway, I really appreciate your help, and WILL be reading more in the future.

Thanks all,
Larry

 

[polyvue]

Ok, I reopened it today, the refill took, but my CH is only 60ppm so I am trying to raise that. Paul, sorry about Ch vs CH, I didnt realize until reading more the use of CH. BTW, is there a 'BBB' way of raising hardness?

You betch'a. See pool-school/recommended_pool_chemicals

I am unsure of how much bather load the Auto-controller can handle, should I get in the habit of loading tabs into the skimmers prior to the weekend? The pool is not monitored over the weekend, maybe we will have to revamp schedule to have a chem add on weekends if necessary?

Tabs can be acidic so would caution against adding to skimmer... perhaps other members will have a different opinion on this. Also, be sure any weekend additions of compound chemicals are introduced knowing exactly what is being added. Trichlor and Dichlor will provide CYanuric Acid (CYA), Calcium Hypochlorite will add calcium. All of these will also increase Free Chlorine, of course.

The state allows CYA but I don't have any, I thought it was naturally occurring until reading more. This is used as a stabilizer??? And how much do I need?

CYA = Cyanuric Acid = Stabilizer or "Pool Conditioner". You can procure Cyanuric Acid in buckets (4 lbs and larger) or rely on a limited program of Trichlor/Dichlor to increase the CYA. I believe chem geek recommends about 20 ppm for indoor pools.