Rental Pool doesn't register chlorine

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The family that is renting isn't bothered by the light algae on the bottom of the pool, and I'll be sweeping off the algae from the sides, today. They continue to use the pool, especially with our temps in the 100s. If I find the chlorine drops quickly, I'll have him put in more bottles every night and then buy more concentrated bleach when we run out. There is no way I'd be able to use 66 gallons of bleach at my home, so I might as well put it into the pool. That's the reason I had him put in 18 gallons the night before my testing. The pool went from 0 FC to 7 with the 18 gallons, so I guess it would take 3 - 3 1/2 gallons of this chlorine a night to maintain it at a safe level. I am concerned about the low pH, as I don't want the copper pipes to dissolve again. Your calculator recommends I add 126 oz (nearly 8#) of soda ash. Since I have soda ash left over from before, I'll put that in the pool today and see how the pH changes. If I can maintain the pool to just have the light algae on the bottom, I'll be happy. I'll continue to use Pool Perfect with Phosfree, as that seems to help keep the algae down, also. Any other suggestions would be appreciated.

I'm surprised I'm not getting more calls on the re-plastering. I reached out to the 6 top-rated plasterers, and one said they don't come to my area, one said they'd get back to me after reviewing your guidelines, while another is ready to come out and look at the pool and give a quote. People seem to love or hate plasterers, so no one has only positive reviews. It is an expensive gamble, so I hope I choose the right company. One recommended company actually has videos of all their steps online, yet I am concerned with their use of water while troweling the plaster (something your site says weakens the plaster). The guy who is ready to come see my pool said that pool is pebble, so the process is different. I'd still question spraying with a hose so haven't contacted them. Here are the videos showing his process. Step 4 video shows them using a hose while troweling. http://www.reyespoolplastering.com/Construction.html
 
Rental Pool said:
I have to rush back to work, but I wanted to post the numbers. I had my tenant put 18 gallons of bleach in last night. Here are today's readings:
CYA 540 had to do 5 cups tap + 1 cup pool to get 90 (90 X 6 = 540)
FC 7.0 (35 X 0.2)
CC 0.4 (2 X 0.2)
pH 7.0 10-11 drops of R-0006 to get to 7.4
Alk 170 (17 X 10)
CH (tap water 230) pool 60X25 = 1500
Click to expand...
Wow, you hit the jackpot with the CYA - yikes. And with CH too!

As for pH, that is a lot of base demand drops to get to 7.4, so I'm guessing you're lower than 7.0 on pH. I'll post again later after I look at my K-2006 booklet and at PoolMath...
 
Soda ash will raise the TA more than borax will. That TA is already pretty high, so the pH should naturally come up. Are you sure no Dichlor was added? That is acidic.

Not sure why you think 3 bottles will maintain a safe level. With the very high CYA, I think the FC would also need to be much higher to effectively kill pathogens in the water .... And killing algae would require even higher FC levels.
 
Looking at the Taylor book (for how much sodium carbonate to add for 10 drops base demand) and correlating with what PoolMath says about the results of adding sodium carbonate (soda ash), I'm coming to the conclusion that you are about 1 point low on pH - in other words, 1 down from the 7.4 goal you went up to with the base demand drops. So your pH looks like it is well below 7. This is all approximate, so add borax in partial doses to bring it up, and measure between additions.

I agree it is hard to know what chlorine levels you need for killing pathogens, never mind the higher levels to address algae. If the algae quickly consumes the chlorine, levels would keep dropping below those pathogen-killing levels. Hopefully your tenants are well informed about risks they may be taking (even if they're ok with a little algae).
 
With a CYA of 540 ppm, a high FC would have some of the chlorine bound to CYA be counted for disinfection and oxidation, though not very much. In theory ignoring the chlorine bound to CYA our minimum FC would be 40 ppm, but in practice especially with the lower phosphate levels from the PhosFree the practical minimum is probably no higher than 16 ppm (about a 3% FC/CYA ratio). Of course, that is not talking about a SLAM and getting rid of algae clumps, but only about inhibiting algae growth.

I think you're being only in the 7 ppm FC range is allowing algae to still grow slowly and that creates a higher chlorine demand. If you were able to get ahead of algae growth, then you could get to a lower chlorine demand, even lower than the fairly typical 2-3 ppm FC per day because your FC/CYA ratio will be lower than our normal minimum. In theory, you should be able to get to around 1 to 1.5 ppm FC per day -- IF you get ahead of algae growth. However, that's going to require chlorinating liquid or bleach addition every day to maintain around 16 ppm FC -- there's no way around that without automation.

Clearly water dilution is going to be required for this pool to lower both CYA and CH. Even if you don't use RO, you should plan on using every drop of rain this winter to dilute the water so do a partial drain with every rainstorm, if possible. Using a pool cover would virtually eliminate evaporation to conserve water throughout the year (and help prevent CH buildup as well), but that's a separate issue.

I want to remind you that the CYA counts towards TA so your target TA range is actually going to be on the high side. At a pH of 7.5, the CYA contribution to TA would be 173 ppm so your TA target for a balanced CSI would be 210 ppm (this has 34 ppm carbonate alkalinity). You could go higher, say to 250 ppm, but not much lower. However, at a pH of 7.0 which is what you reported, this changes dramatically where the CYA contribution to TA is 132 ppm so your TA of 170 is around 38 ppm carbonate alkalinity so OK. Overall the CSI is -0.35 so not a disaster, in the short-term but will get better as the pH rises and as you point out you don't want low pH for very long since it is also corrosive to metal.

I would NOT use a lot of soda ash to raise the pH because that will raise the TA by too much. If you were to use 126 ounces weight (about 8 pounds) of soda ash, your pH would rise to 7.2 (if it were really 7.0 to start with) but your TA would rise from 170 to 215 and your carbonate alkalinity from 38 to 61 ppm. That's probably the most you'd want to do and would bring you overall to a close to balanced CSI (+0.06). You can go ahead and do this, but don't add any more. If you need to increase your pH more than that, you should aerate the water.

Using chlorinating liquid or bleach will probably have the pH slowly rise over time. An alternative to using the soda ash would be to use 20 Mule Team Borax where you'd add 252 ounces weight to get to that same 7.2 pH, but the TA would only rise to 195 ppm in this case (carbonate alkalinity stays about the same from 38 to 40). This would also add 10 ppm Borates to the pool. If you were to eventually add more borates to get above 30 ppm and closer to 50 ppm, then they would not only buffer the pH but act as an additional mild algaecide. The point is that using Borax is probably a better choice except for the fact that you've already got the soda ash.

Obviously with this pool you can't look at our Recommended Levels and have to instead focus on two things: the pH to not be too low to be corrosive and the CSI to prevent plaster deterioration or scaling (which mostly means not letting the pH nor TA get too high). A reasonably balanced CSI will also take care of having enough carbonate alkalinity for pH buffering against net acidic chemicals.
 
As noted in that thread, the main issues are that 1) it's not easy to go back to a chlorine pool once you've turned it into a bromine one and 2) bromine breaks down in sunlight so if you don't use a pool cover you could end up using more oxidizer (e.g. chlorine) than you would if you just stayed with chlorine.

There is absolutely nothing wrong with having the rental stick with chlorine and maintain a high FC level for that high CYA level. Once algae is gone, it should work as well as any of our pools except to keep the FC/CYA lower the phosphates are being controlled. It should actually end up being less expensive to maintain if the chlorine usage does get to about half what our min. FC/CYA pools use so long as there are not large additions of phosphate (such as with HEDP metal sequestrants).
 
Chem Geek, the OP reported that it took 10-11 drops of the K-2006 base demand reagent to get from the 7.0 color (7.0 is the lowest on the Taylor color scale) to 7.4 - if my reasoning (above) is valid, that would appear to put the initial pH well below 7.0. What effect would that have on contribution of CYA to TA and other aspects of the chemistry you discussed?

Are you saying that it is possible under some conditions (including keeping phosphates very low) to reach a sort of co-existence with a modest amount of algae - inhibiting it's further growth, but without killing it off either? I'm just curious, since this pool has very unusual conditions compared to most seen on the forum.
 
10 base demand drops is equivalent to 3.20 pounds of soda ash per 10,000 gallons. If it would take that much to get the pH to 7.4, then that doesn't even add up since with the numbers reported it would only get the water from 7.0 to 7.17 so around 7.2, not 7.4. It would take around 7 pounds of soda ash to get to 7.4 so more like 20 drops of base demand. So something is off somewhere in the numbers. The water seems to be behaving as if there isn't as much buffering as reported or the starting pH is actually 7.1 in which case the 10 drops would represent soda ash getting one to 7.3 which sounds plausible.

So it seems to me that the pH is actually around 7.1 and not below 7.0 so I'd treat the water assuming that so one does not overdose on raising the pH.

As for the lower phosphates, no I don't mean co-existance with some algae. I'm talking about getting rid of it completely by having a sufficient chlorine level, though lower than we normally recommend. If the FC is raised now to something like 20 ppm, then with the low phosphates the algae even in small clumps may get killed faster by chlorine than they can reproduce. This may not happen quickly, but given that this pool seems to be doing better now than in the past it seems plausible that keeping a higher FC level than has been done will be enough to eventually kill off the algae and then maintain at FC 16 ppm or thereabouts. It won't be fast as with a SLAM, but it could happen over time, especially with some brushing to break up the algae clumps. Given the very limited options with this pool, it's something worth trying.
 

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I wish I had known how much the alkalinity would rise using soda ash. Hopefully it won't be a problem. Before I give the new numbers, let me point out I don't believe there is any remaining algae, though the plaster seems to be stained where the algae was.

I had my tenant put in 2 gallons of bleach last night, but asked him to boost it to 4 gallons per night from this point on. Here are the results:

FC dropped from 7.0 to 2.2, with CC at 0.6 (though it may have been 0.4 -- didn't want to rerun the test for .2).
I added 4# of soda ash, and the pH went to 7.2 with 8 drops to 7.4.
Alkalinity jumped from 170 to 320.

The tenants say the pool looks great, so I just want to maintain it till the weather cools down and I can replaster the pool. I guess it is best to wait till I have the new plaster before installing a SWG. I'm not looking for perfect, but merely to maintain for another few months. I appreciate all your suggestions. I'll check it again tomorrow to see the impact of 4 gallons of bleach.
 
According to PoolMath, I was told to put in 7.898# of soda ash to bring the pH from 7.0 to 7.4, so I decided to cut it in half and let it rise only to 7.2 (which it did), especially since I didn't know how great an impact it would have on alkalinity. I'll let you know tomorrow if the remaining soda ash in suspension dissolves and changes anything.
 
chem geek said:
10 base demand drops is equivalent to 3.20 pounds of soda ash per 10,000 gallons. If it would take that much to get the pH to 7.4, then that doesn't even add up since with the numbers reported it would only get the water from 7.0 to 7.17 so around 7.2, not 7.4. It would take around 7 pounds of soda ash to get to 7.4 so more like 20 drops of base demand. So something is off somewhere in the numbers. The water seems to be behaving as if there isn't as much buffering as reported or the starting pH is actually 7.1 in which case the 10 drops would represent soda ash getting one to 7.3 which sounds plausible....
Click to expand...
I'm confused by a couple of things. I agree that the 10 drops base demand corresponds to 3.2 lbs. soda ash into 10,000 gallons, according to the Taylor chart. I couldn't figure out where your 7.0 to 7.17 estimate came from at first, but I think you were looking at the effect of 3.2 lbs. in the OP's 20,000 gallon pool, rather than in the hypothetical 10,000 gallons on the base demand chart. That factor of 2 difference explains some of it.

That still leaves me really confused about the part of PoolMath I was looking at earlier, prior to my claim that the pool pH might be well below 7.0. If I go to the applet at the bottom of the PoolMath page, to look at effects of adding chemicals, and put 51 oz. soda ash into 10,000 gallons, it says that will raise pH by 1.11. Why is that number so far off from what the main part of the calculator says?

Is the chemical effects applet totally free standing; i.e. that it pays no attention to the pool parameters (other than volume) entered in the upper part of the calculator?

Original poster, I apologize for adding confusion to your thread - that was not my intent.
 
No problem singingpond. I wish more people would take the time to seek clarification so they can truly understand others (rather than just make assumptions).

By the way, I forgot to mention, but I tested my TDS, also, and came up with 184. That actually seems very low considering the rest of my pool chemistry. Later today, I'll report today's numbers, but won't have new numbers till Thursday.
 
Well, I hope you keep posting and asking questions! Your pool is unusual enough in its chemistry to be quite interesting. What is going on in there will be hard to understand and predict for most of us on the forum, as you are pretty far away from the familiar chemical ranges for CYA and CH. So, pay special attention to Chem Geek (and one or two other posters, myself not included) who actually understand the underlying chemistry in a more than superficial way.
 
singingpond said:
I'm confused by a couple of things. I agree that the 10 drops base demand corresponds to 3.2 lbs. soda ash into 10,000 gallons, according to the Taylor chart. I couldn't figure out where your 7.0 to 7.17 estimate came from at first, but I think you were looking at the effect of 3.2 lbs. in the OP's 20,000 gallon pool, rather than in the hypothetical 10,000 gallons on the base demand chart. That factor of 2 difference explains some of it.

That still leaves me really confused about the part of PoolMath I was looking at earlier, prior to my claim that the pool pH might be well below 7.0. If I go to the applet at the bottom of the PoolMath page, to look at effects of adding chemicals, and put 51 oz. soda ash into 10,000 gallons, it says that will raise pH by 1.11. Why is that number so far off from what the main part of the calculator says?

Is the chemical effects applet totally free standing; i.e. that it pays no attention to the pool parameters (other than volume) entered in the upper part of the calculator?

Original poster, I apologize for adding confusion to your thread - that was not my intent.
Click to expand...

Nope, I used 3.2 pounds in 10,000 gallons, not 20,000 gallons, using the pH of 7.0, TA of 170, FC of 7.0, CYA of 540, CH of 1500. However, you cannot use PoolMath for this because the numbers are way out of the range where it can do pH calculations. I used my Pool Equations spreadsheet. pH calculations are very complicated so PoolMath uses table lookups and interpolation for reasonable pH and TA and CYA ranges. The TA and CYA are way out of the norm so the calculations in PoolMath are not correct. The calculations in my spreadsheet are correct but very complex.
 
I was very careful about the drops. Here are new pictures and chemical numbers:

FC = 2.6 (from 2.2 yesterday with 4 gallons of chlorine added last night -- should I ask tenant to only put in 3 gallons a night or keep it at 4 gallons and see what it is like on Thursday?)
CC = 0.8 (from 0.6 yesterday)
pH = 7.2 & 7 drops to 7.4 (from 7.2 & 8 drops yesterday)
Alkalinity - 190 (170 on Thursday, 320 on Friday, so it is dropping back down)

The pictures don't show any algae, though it appears to show stains where the algae used to be.
https://www.dropbox.com/sh/bmm1j14f22xdbs6/AACrvWkuK7Wzm3DiTQ1IaAxea?dl=0

Do you recommend I just maintain it as it is till I re-plaster the pool, or do you have concerns I need to address? Thanks for your help.
 

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