PH dropping WHY

[idowatsu]

Please help! OK I have been putting this off,I have a serious problem with falling PH levels in my pool that has been ongoing for about 8 months or so. The acid pump has been shut off for at least 6 months. I have learned my lesson with leaving the PH at 7.4 to 7.2 having had to recently replace a heater from corrosion.(other problems too).It's been dormant since November to fix the heater. Finding someone to do it here is tough.
Starting the pool back up now, need some help with the long term ORP problems too, this system was quite stable previously.
I have a low level algee problem that I might have to find a new ladder to get rid of (it collects in the struts on the back side and is hard to clean). the ORP drops from 685 to 445 in the 10 hours the pump is off at night.Even when the TA was at 80 it did this. Before the ORP stayed between 650 and 720. Filter is always clean, light bather load.
FC 1.2
PH yesturday 7.6 after adding PH up the day before.today 7.3
TA 140 I will start gassing today to bring that down.I use a blower wand on a shop vac tied to the ladder.
CYA 0 indoor pool. it effects the reading on my chemtrol.
calcium never an issue I think it is always steady at 120.

This is as much info as I can give you at this time. Kim :?

 

[JasonLion]

What are you using as a chlorine source? Also, what chemicals are used with the pool on a daily, or every other, basis?

 

[idowatsu]

as my signature says I have a SGW and acid pump automated with a chemtrol.Acid's been off for quite some time. Dont add anything if I can help it. A dab of phospate remover back about a year ago when the SGW seemed to not work. (phospate from laundry soap eating up the chlorine) manufacturer recommended to try this , got a test kit at the fish store and found it was the problem, that was then fixed.
The pool had been down 2 months for repair, two weeks ago I did a dose of chlorine free shock but didn't follow up because it wasn't totally fixed. that worker was a licenced pool person but wasn't fixing it right. I finally called my do everything guy to fix his mess.
I have been using in the last week GBL PH up 2 doses and an oz of GBL clear blue. I normally never add anything but acid. and adjust the chemtrol to keep the FC correct. I did 24 hrs. of gassing off about in october. Brought TA from 120 to 80 then.
Haven't been using the ion generator till I discovered the algee problem turned it on a couple days ago. I know it takes a while for it to be effective. I had problems keeping it below the proper level(not automated)which builds a copper residue and dosen't go away without draining. the Ion level is 1 way high.I forgot and left it on oops.looks like I will be adding some metal remover.supposed to be .3 might have to drain some of pool.

 

[chem geek]

You shouldn't need to worry about lowering your TA so soon if you are still experiencing a rapid pH drop. The higher TA can only help to reduce that drop. Unless your Calcium Hardness (CH) is high, you shouldn't worry about a higher TA level when you have a situation where the pH is stable or dropping.

Since your pool is indoors, are you keeping it covered with some sort of pool cover that is on most of the time? If so, then that prevents outgassing of carbon dioxide that would otherwise tend to make the pH rise and compensate for whatever is lowering your pH. Or course, you probably don't want your pool to be uncovered for too long since that increases humidity in the room.

Your situation is very strange since a saltwater chlorine generator pretty much always leads to a pH rise, at least somewhat if not a lot. I suspect that you still have some sort of acid addition and that is causing the pH to drop. The Chemtrol 250 automated chemical controller is possibly broken and stuck "on" for feeding acid or maybe the Mecomatic acid feeder is broken (leaking acid).

Your ion system probably isn't affecting pH, but I'd turn that off if it's on for any time. Use chlorinating liquid or 6% unscented bleach to shock the pool to get rid of algae.

Remember that if your chlorine level was very high and then dropped a lot, that will also lower the pH -- but it's a one-time drop and adding more chlorine would have the pH go back up unless you used Dichlor or Trichlor (which you shouldn't be using).

As for the corrosion in your heater, this is probably due to a combination of high salt levels (needed for the SWG) and no CYA in the water. If your pH only dropped to around 7.2, then that probably didn't cause problems with the heater. Though CYA would have the Chemtrol read a lower ORP level at the same FC, you could probably just have a higher FC setpoint. For example, you could use 4 ppm FC with 20 ppm CYA and that should read the same as 0.2 ppm with no CYA and both should read about 716 mV on a Chemtrol or 681 mV on an Oakton. Did you ever test your FC level at various ORP levels to see the correlation?

Finally, I don't understand how you got algae in your pool unless the FC level dropped. Your rapid overnight ORP drop when the pump is off is the same as having the FC drop and it's a lot. This does indicate algae growth and as stated above you should use manual chlorine dosing to shock the pool to get rid of it. Maybe the drop in pH is associated with the killing of the algae, but if you shock the pool to kill the algae then you can see whether you still see a pH drop even after disconnecting the acid feeder.

Richard

 

[idowatsu]

I keep the salt level a little low at 2800 ppm , I did overflow the pool recently buy a lot and had to add more salt.
I am in the middle of gassing at this time.
Cal has never been an issue it has remained a constant 120
the acid pump has been switched off for about 5 months.
humidity isn't an issue, the ventalation is really good. the cost of heating is though, didn't know how much a 1hp pump cost to run till it's been off for a couple months now.
Just went down to a 250,00 BTU heater from a 400,000 one.

TA 1.2 at 653 ORP
the TA tested 1.5 or so at 670 ORP but the generator was on.
we'll continue this in a couple days. but I dont think any of your suggestions are it.
algee is accumulating behind ladder between struts in steps. no matter what I do, time to find a new ladder for vinyl pool any suggestions.

 

[chem geek]

When I say "high salt level", I don't mean for a typical saltwater chlorine generator pool. I mean relative to a pool that does not have an SWG. In other words, having an SWG requires you to have a much higher salt level than would be found in a non-SWG pool. If you combine that with the high active chlorine concentration due to having chlorine with no CYA in the water, then this is a much more corrosive situation, especially if your heater used a copper heat exchanger instead of something more corrosion resistant such as cupro-nickel or titanium. If you are getting a new heater, try and get one that has a corrosion-resistant heat exchanger.

I assume that the acid feeder is like the SWG in terms of both being placed AFTER the heater so it goes Pool --> Pump --> Filter --> Heater --> SWG/Acid --> Pool is that correct?

So does your comment about humidity not being a problem mean that you are not using a pool cover? In this thread you mention having a pool cover.

When you say that a 1 HP pump costs a lot to run but that it's been off for a couple of months now, how are you getting circulation and filtration of water in your pool? The SWG won't be generating chlorine if the pump isn't running so how was the pool chlorinated with the pump off?

When you say "TA" in your post, I believe you mean "FC". If having an FC of 1.2 ppm only measured 650 mV ORP and this was before you had your algae problems, then your controller is probably not functioning properly or you have some CYA in the water. Normally with that FC and no CYA you would get more like 750 mV ORP or more (see Figure 3 in this Chemtrol PDF file). If you had 10 ppm CYA then that could result in 650 mV ORP though this varies a lot by sensor. In this post you mention that you removed the CYA because it was interfering with the Chemtrol -- how did you do that? Did you do a complete water replacement or just dilute the water down until the Chemtrol seemed to work?

You have algae growth so read Defeating Algae in the Pool School. You do not get rid of algae quickly by using an SWG alone. Though it is getting killed somewhat when the SWG is on during the day, the algae comes back at night when the SWG is off. If you had a shock level of chlorine in the water, then this would kill the algae 24/7. Of course, shocking your pool with no CYA in the water is tricky since it's even more corrosive though only for a relatively short time (probably less than a week). Part of the problem is that the circulation around the ladder is probably poor so the FC runs out locally near the ladder when the algae grows at night. Since you were reporting such large ORP swings even in this post, this does not seem to be a new problem and you could have had algae growth back then in October. Jason surmised as much and suggested you check the FC loss overnight but you never responded back. It's also not clear whether you ever added borates.

When you say you are gassing, do you mean you are aerating the water (and maybe adding acid unless the pH isn't moving much) to lower the TA? Why are you doing that?

I am unclear bewteen the "cedar sides" and the "vinyl lined" (in your signature) what is in contact with the water in your pool. I've heard of cedar wood being acidic so if it's in contact with the water then that might help explain the continued drop in pH over time.

I don't have any suggestions for a ladder; perhaps someone else has some ideas for that.

Richard

 

[dschlic1]

If you have a continious problem with a low level algea infection, Then I recommend that you shock the pool (as described in the pool school), and while shocking, try and backflush the pool water through your air piping. This will clean and disinfect the air piping in your spa jets. I had a similiar problem. It may not be your ladder.

 

[idowatsu]

Hi Richard thanks for hanging in there with me. I haven't got to adding borates yet.
You might have had something with the leaving the cover on too, it had been left on a lot more in the last 6 months. The room is very well ventelated.
I have been acid adding and aerating it overnight so the pump was on all last night, got the TA down to about 90, much better. I plan on taking the ladder off and cleaning it , needs rescrewing anyway.
The pool has a vinyl liner inside the cedar siding.
yes the acid feed is placed last in the line out to pool.
I noticed the cost to run the pool now because it has been off for the 2 months to fix the heater. all tore apart and that person disappeared mid job, just got it back together :-D
you loose me when you start talking about orp adjustments, it took me a long time to get used to the controler. I am doing a lot better now. Thought I had a faulty ORP sensor but it was something I was doing wrong.thanks for the chemtrol PDF I will try to understand it.
I will use some non chlorinating shock (got another bag) once I have the ladder clean.got to go now I will test the CYA level to see if any got in there and let you know later tonight. Kim

 

[JasonLion]

Keep in mind that using non-chlorine shock (typically MPS) will cause the ORP to read high for up to a couple of days, which will tend to cause the automation system to put in too little chlorine. You need to manually test the FC level and adjust the ORP set point at least once a day, preferably two or three times a day, after using non-chlorine shock until things settle back down and the ORP reading is stable again.

 

[idowatsu]

took the ladder out to see if it was the cause of the ORP drop, but it read 450 on start up after being off for 10 hours.I brushed and vaccuumed the pool before it shut off last night. the FC level went from 2 last night to 1 this morning.
The shock is GLB oxy-brite, potassium peroxymonosulphate

The ladder looked like the constant low ph had dissenigrated it I sprayed off these jelly-like deposits on the back and went to wipe it down and a white chalky substance kept coming off, my hands dried out from it really bad.I purchased a stainless rail plastic step above ground ladder with swivel bottom for the sand edge of the liner.hoping it will be better to clean.

 

[JasonLion]

I wouldn't normally expect the ORP reading to be correct when the pump was off, unless the ORP sensor system has it's own pump (and even then it won't be as accurate when the pump is off). It will also take several minutes after the pump is turned on for the ORP reading to become correct again. On the other hand, while the ORP reading won't be accurate when the pump is off, it shouldn't vary as much as what you are seeing.

If I am following correctly, you appear to have a low level algae problem and a SWG. It is fairly common for a SWG to be able to hold algae off, never completely killing all of the algae yet never allowing the algae to really grow out of control. In that situation, it makes sense for the algae to consume all of the chlorine while the pump is off, and for the chlorine level to rebound when the SWG turns back on.

Have you tested the PH and TA of your fill water? Low PH fill water and an autofill system, while unusual, could account for the PH constantly dropping.

 

[idowatsu]

filling is done by hose and I have flooded the area severely about 4 months ago did it a little a couple days ago. Tested the salt level it's still 2800ppm according to the guidelines on this site keeping it at 3200 would be better.
so the PH has dropped from 7.7 to 7.5 in 48 hours. I turned the feed back off but it was set for 7.7 so I don't think it kicked in. I did get into pool for about 30 min to vaccuum last night. I also pulled out the ladder but I had to put it back tonight till I get the new one.
I get the low level algee thing I thought removing the ladder would help it. Is it in the piping in the pump room and how do I get it out?will adding Borates bring this problem to an end?I have been thinking of doing this for a while.

 

[dschlic1]

Here is the procedure I use to flush the air piping on my therapy jets:

I remove the nozzole assemblies and replace them with a pipe plug. The nozzles are standard eyeball return fittings that screw into PVC fittings cemented to the pool. In my case the pool fittings have 1 1/2" NPT threads.

I remove the screen from the air inlet pipe and connect a hose to it leading back to the pool. My air piping is standard 1 1/2" PVC water pipe. It has an OD of about 2".

I switch the filter to spa mode. This causes the filter water to pass through the therapy water piping and then up through the ait piping. Filter preassure does increase substantially. I run the system in this mode for about one hour each month.

If your spa jest use a blower, you will have to remove it inorder to perform this procedure.

The problem with spa or therapy jest is that part of the air piping is flooded with pool water when not in use. This water is not circulated, and may remain static for days if not weeks. Also if your pool level varies the level of water in the air pipe will also vary. These condition lead to poor santation in the air pipes of spa or therapy jets even when shocking the pool.

 

[idowatsu]

Been lurking on forum for a couple weeks frequently. bless RSS feeds I have it on my home page now.
Sooooo I still have the low level algae problem. I did add borates. holding steady at 50. the orp # are around 715 when the pump shuts off and 450 in the morning, as well as the PH at 7.8 when the pump starts then drops to 7.6 after it runs for a couple hours. I have had the acid pump off for over a month now and it has only raised .1 from a range of morning 7.7 to 7.5 . Today I started a bleach shock according to the pool calc. but didn't get the right test kit first, cant order for another week, had to close the credit card and get a new one. so I'm stuck till I get it. Do you maintain the clorine level at 10 throughout the shock period? and how long does it take till you can return to getting in the water. Indoor, no CYA (screws up the chemtrol reading)

 

[JasonLion]

Yes, you want to maintain FC at shock level through the shock period. You should also brush the entire pool at least once a day while you are at shock level.

Once the algae is dead, it will take several days, possibly more, for the FC level to fall to more reasonable levels. Depending on how much you normally use the pool, you might want to use a chlorine neutralizer.