using citric acid to remove metal stains...

Hi everyone,

I read several threads on here about removing stains and really appreciate the knowledge stored here! I brought my Chlorine level down low (0.5-1ppm) last weekend, added polyquat and about five pounds of citric acid on Saturday - roughly following mbar's sticky. It's taken a couple of days but most of the stains are finally gone. There are a few stubborn old ones still on seat area but nearly all of the ones on the walls have disappeared.

Following PoolDoc's advice to someone else on another thread, I've begun adding Chlorine while keeping the pH at about 6.8. So far the Cl reading keeps going back to zero, even with the saltwater generator running. My main question is whether I should add a trichlor puck to the skimmer? (Another bit I picked up in another thread that I understood to mean it can help precipitate out the metal to catch in the filter.)

I should have mentioned that I've also put in "PoolTime" brand Metal, Stain & Scale out per the instructions on the bottle - which means 2.5 32oz bottles. The idea of course is to keep the metals in solution as the Cl goes up. My CYA is about 40 last I checked. The pH falls whenever I add water to the pool, so I usually have to add 1/2 gallon of muriatic acid at the same time. Also, if it matters I do have a pool heater but we've never used it. It's been four years since we had the pool refurbished (fiberglass coating over concrete) and metal stains haven't been a big problem. They started to appear as little speckles on the sides last year but I didn't do anything about it until now.

THe polyquat, the citric acid, and the metal sequestrant tend to cause high chlorine demands, so you may have to supplement the SWCG with bleach to get the chlorine to register, at first. If you don't overcome it pretty quickly, though, you may need to shock the pool since keeping the chlorine at low levels for very long will allow algae to bloom. Putting a trichlor puck in the skimmer will add chlorine, assist your metals in precipitating out onto your filter, and keep your pH on the low side, so I don't see a reason why you couldn't use it.

Also, you might want to check your owner's manual regarding your CYA level--I think most SWCG manufacturers want 60-80 ppm of CYA in the water to assist the cell in operating the most efficiently--and low CYA may also be why you're having trouble keeping chlorine in the water...

One statement you made doesn't make sense to me, though--you said that the pH of your water falls when you add new water, so you're also adding Muriatic acid? If the pH is falling, you want to add Borax to raise it--MA will only bring it down further.

Janet

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Originally Posted by river-wear

My CYA is about 40 last I checked.
And you have an AutoPilot SWG. Bring it up to 80 ppm!
While you are at it please post a full set of test results. Right now I am particularly interested in your pH, TA and CH too.

The pH falls whenever I add water to the pool, so I usually have to add 1/2 gallon of muriatic acid at the same time.
Red flag here. Either you mistyped or we have a problem Houston! Exactly what is your pH AND TA right now? If the pH is reading 6.8, which is the lowest a pool test it can read and your TA is low then it is very possible that your pH is MUCH lower than 6.8 and causing damage to your pool. IF so get some borax in there FAST to bring your pH up to 7.2 for now since you just did a stain treatment and then add baking soda in very small amounts to get the TA up to 70 ppm if it is below that.


Also, if it matters I do have a pool heater but we've never used it.
If you pH is a low as I suspect it might be you could have a problem if you heater uses a copper heat exchanger. If the pH is low get your water tested for copper.

It's been four years since we had the pool refurbished (fiberglass coating over concrete) and metal stains haven't been a big problem. They started to appear as little speckles on the sides last year but I didn't do anything about it until now.

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What color? Were they black? That is cobalt spotting (cobalt leaching from the gelcoat and crystallizing on the pool surface). Best preventative is to keep the CH as high as you would for a plaster pool. No guarantee that it will work however, much depends on the quality of the gelcoat they used on the pool.

OOPS! So sorry - the pH INCREASES when I add water. I'm not crazy, just goofed. :o

I'll run full tests tonight to see where everything is. I have not had any problems keeping the Cl level up all summer, and (knock on wood!) haven't had any algae problems either. I expect TA will be on the high side because in the past I've had to run the spa with bubbles to bring it down - that is the one that needs aeration to lower, correct? I'm a little fuzzy on details because things have been running smoothly with pool for a couple of years and I forgot some of what I learned here before.

In addition to putting the puck in the skimmer last night (and leaving the SWG running as usual), I also added about a quart of liquid Chlorine to bump it up. We'll see how much effect it had when I get home from work.

Waterbear: dumb question for you - does the water always circulate through the heater even when not in use? At least in a standard setup? I imagine different pools could be plumbed differently. I'm not sure so I'll have to look at mine, but I had assumed (yikes) that it was bypassed when not used.

In answer to your question - the spots were orange. I'll look into the CH (Calcium hardness, right?) to prevent new problems from cropping up though. I know the city water here doesn't typically have a lot of mineral content. If I need to increase it, how is that done?

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Originally Posted by river-wear

OOPS!

Waterbear: dumb question for you - does the water always circulate through the heater even when not in use? At least in a standard setup? I imagine different pools could be plumbed differently. I'm not sure so I'll have to look at mine, but I had assumed (yikes) that it was bypassed when not used.
Yes, normally, unless you have a bypass plumbed in and you turn the valves to bypass the heater. This is the exception rather than the rule since heater damage can occur if fired up with no water flowing through it.

In answer to your question - the spots were orange.
That would be iron
I'll look into the CH (Calcium hardness, right?) to prevent new problems from cropping up though. I know the city water here doesn't typically have a lot of mineral content. If I need to increase it, how is that done?

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Hope this helps

I figured it was iron, but for the sake of curiosity, what color are copper stains? Green?

Here are the full test results for today:

Cl - zero again; added 1/2 gallon of 10% chlorine (sodium hypochlorite)
pH - 7.2
alk - 60
Cal - 220
CYA - 50
salt - 2800ppm per test kit (AutoPilot says 3600...)

What are the desired levels for alkalinity and calcium?

There's still a puck in the skimmer and the chlorine generator is doing its thing, so I didn't want to add too much more of the liquid. I'll check on it again tomorrow. The water is clear and blue, but it feels like I'm tempting fate by writing that. ;)

I still have a few stubborn stains in one spot, but all of the little speckles have disappeared now. Is there something you'd recommend for spot-treating?

Thanks!

I have a Hayward CZ 250 heater and it has a flow/pressure switch which detects water flow. If I do not have water flowing through my heater, the heater will not ignite. I also put in two valves that control water flow to the heater and also used to bypass it. This is a good idea in the Spring as water usually needs to be balanced and has crud in the flow. Also, during the summer months, when you do not need the heater, there is no reason to have water running through your heater. Doing so just exposes the heat exchanger to possible damage if you run unbalance water through the heater for an extended period of time. The damage is usually due to the copper in this unit. Trust me. I have already replaced one heat exchanger and it was expensive. Two cheap valves can eliminate most of the risk.

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Originally Posted by river-wear

I figured it was iron, but for the sake of curiosity, what color are copper stains? Green?
Green, blue, black, grey, brown (copper color). Black and grey are the most common colors on fiberglass.
Here are the full test results for today:

Cl - zero again; added 1/2 gallon of 10% chlorine (sodium hypochlorite)
pH - 7.2 bring this up to 7.6 slowly once your stain treatment is finsihed and all stains are gone
alk - 60 bring it up to 70 ppm
Cal - 220 bring this up to 400
CYA - 50 bring this up to 80
salt - 2800ppm per test kit (AutoPilot says 3600...) What kind of test? I would tend to trust the Autopilot on this since that is what the cell is actually measuring. It's still withing the operational range so nothing to lose sleep over.

What are the desired levels for alkalinity and calcium?

There's still a puck in the skimmer and the chlorine generator is doing its thing, so I didn't want to add too much more of the liquid. I'll check on it again tomorrow. The water is clear and blue, but it feels like I'm tempting fate by writing that. ;)

I still have a few stubborn stains in one spot, but all of the little speckles have disappeared now. Is there something you'd recommend for spot-treating?
Put some vitamin c tablets in an old white sock and hold them on the stains.
Thanks!

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Hope this is helpful. The numbers I gave you above will have your water 'balanced' even if the pH drifts up to 8.0, which happens with SWGs so you should not have any bad scaling conditions. It is a bit aggressive at a pH of 7.2 but you want aggressive water when dealing with stains. At pH of 7.6 to 8.0 you are golden and that is where I would recommend you run the pool. Don't let the pH rise above 8.0 nor drop below 7.6 in normal operation and you will be golden.

Thanks for the help, Evan. I'll doctor things up to get a better balance. Maybe I won't have to be adding acid quite as often if the water is buffered better. I do usually run the pool at a pH of 7.6. One question though - why so high on the CH?

You asked about the salt - I used one of PoolDoc's test kits for that. I think it's more accurate because when I was relying on the Autopilot last year (too lazy to test), the chlorine just didn't seem to keep up with demand and I had to put the SWCG on the highest power setting. Now, with the higher salt level I put it back down to the "normal" power setting (there are three) and the water has been clean & clear all summer. In any case, it's in operating range as you pointed out; it just seems to run better/more efficiently now. I also read that the Autopilot will read the salt levels with varying accuracy depending on the temperature of the water.

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Originally Posted by river-wear

Thanks for the help, Evan. I'll doctor things up to get a better balance. Maybe I won't have to be adding acid quite as often if the water is buffered better. I do usually run the pool at a pH of 7.6. One question though - why so high on the CH?
To keep the water balanced with the other parameters I gave you since you have a plaster/fiberglass pool. I kept your Saturation Index within 'range' with a pH range up to 8.0 so you don't develop scaling conditions and there is some evidence higher CH can help prevent fiberglass staining. The parameters I gave you for CYA, pH and TA are to minimize your acid demand.
You asked about the salt - I used one of PoolDoc's test kits for that. I think it's more accurate because when I was relying on the Autopilot last year (too lazy to test
I am going to assume this includes all tests including pH and CYA, correct?), the chlorine just didn't seem to keep up with demand (sounds like low CYA) and I had to put the SWCG on the highest power setting. Now, with the higher salt level I put it back down to the "normal" power setting (there are three) and the water has been clean & clear all summer.
Did you raise your CYA?
In any case, it's in operating range as you pointed out; it just seems to run better/more efficiently now. I also read that the Autopilot will read the salt levels with varying accuracy depending on the temperature of the water.

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Understand that the Autopilot is meaureing conductivity and not chloride ions like a chemical test. While the two are usually in the ball park they are not the same and for the sake of a SWG operation it's interested in the conductivity of the water and nothing more.
(Poolsean, Please correct me if I am wrong on any of this)
As far as the PoolPilot power settings, these should have nothing to do with salt level UNLESS you are running your salt way too low or unless your cell is fouled with calcium deposits and needs cleaning and cannot generate enough chlorine. The salt sensor in the AutoPilot is temperature corrected, which is why your cell output seems to fluctuate somewhat with temperature. My question for you was where was your CYA when you had to run at the higher power level? Low CYA is more likely to cause needed to bump the power than any other reason. Evan now at 50 ppm your CYA is too low and you should raise it to 80 ppm. This will translate into lower output setting which will translate into less CO2 outgassing which translates into more stable pH. The lower TA is also to lessen the outgassing of CO2. Ditto for not allowing the pH below 7.6 in normal operation. The lower you put the pH the faster you outgas CO2 and the faster pH rises.

Interesting stuff, thank you!

Today I picked up the baking soda for raising TA, and will get the CYA and calcium tomorrow.

No, I wasn't too lazy to test other things last year. :p I just skipped the salt test. Last year I ran the Autopilot with it reading 2800-3000ppm (now it's 20% higher).

My CYA is about the same as it was last year. I added some this spring because the pool overflowed with a bit with the winter rains, diluting it. That's why I had to add quite a lot of salt too. In any case, I will bring it up to the recommended levels.

Be sure to only raise the TA by 10 ppm. You want to keep it at 70. (You could also just leave it at 60 ppm for now and if and when it drops below bring it back to 70 ppm and not higher! )
You have never said how big you pool is so I cannot help you with dosing info but for everh 1000 gallons a SCANT 1/4 cup of baking soda will be in the ballpark to raise the TA by 10 ppm.
I would put in 3/4 of the amount you need over a period of several days--a small amount each day (because you just did the stain removal and you don't want pH to jump quickly lest the stains return., wait 24 hours after the last addition, adjust pH to 7.6 if it is higher (use your acid demand test if you have one)--If it's lower don't worry too much about it, wait another day your TA.
If it it still too low start adding the remaining 1/4 of the baking soda left over a few days and repeat the pH adjustment and testing.

I would not do this until you have finished with all the stain removal and your chlorine is holding properly.

Pool size is in my signature - 27,000 gallons. :)

I only put in a one pound box of baking soda so far. (The pool calculator site says I'll need five.) I had to add water last night and didn't want to bring up the pH too quickly, just like you wrote. I will hold off until I can get in there with the Vitamin C tablets to finish off my stubborn stains. (And get the chlorine stable.)

I'll look for calcium hypochlorite at the pool store (my once-annual trip, I suppose) to try to hit two birds with one stone. I realize that more calcium will be needed than just what is in chlorine though.

One more thing on the salt readings from the Autopilot vs. using a test kit. I had to look it up to make sure I hadn't "mis-remembered" that the reading will be affected by water temperature:

http://en.wikipedia.org/wiki/Electri...ure_dependence

My water is about 78-80 degrees now. I don't know off-hand what temp the SWG would have been calibrated at. I'm not too concerned about that since I can test once each spring to make sure I'm in the proper range. I really like having a saltwater pool - the reduction in maintenance is wonderful.

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Originally Posted by river-wear

One more thing on the salt readings from the Autopilot vs. using a test kit. I had to look it up to make sure I hadn't "mis-remembered" that the reading will be affected by water temperature:

http://en.wikipedia.org/wiki/Electri...ure_dependence

My water is about 78-80 degrees now. I don't know off-hand what temp the SWG would have been calibrated at. I'm not too concerned about that since I can test once each spring to make sure I'm in the proper range. I really like having a saltwater pool - the reduction in maintenance is wonderful.

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The AutoPilot IS temperature corrected (this is why the output fluctuates in the readout with temperature, it's the temperature correction at work.)
The chromate/silver nitrate test for chloride ions is not without it's own set of problems so it is not the final word either. My rule of thumb, if the two readings are within abut 800 ppm you are certainly in the ballpark. I really don't expect more precision than that nor is it really needed.