Ph Gone Wild!

[Frogspirit]

I am a Certified Pool Operator at a Courtyard Hotel, with a 15,000 gallon pool.

Three days ago the readings and water quality of my hotels inside pool were fine.

Two mornings ago when I came in the water was immensely cloudy with a 0 chlorine reading and a low Ph. I added chlorine (2-1lb. bags of 'Chlor Brite to shock the pool + pucks with the feeder wide open), clarifier (A total of 1 qt. over the day) and 'Alkalinity Plus' (About 3 lbs.).

Yesterday morning the readings were about the same but the water half as cloudy. I added chlorine (1-1lb. bags of 'Chlor Brite to shock the pool) and 'Alkalinity Plus' (About 3 lbs.). I never achieved the desired results for either day.

I've added about five pounds of 'Alkalinity Plus' over the last two days.

Today, o chlorine (However the water much clearer) and a Ph that requires 40 drops of base demand reagent to achieve a 7.6 Ph. Also: Total Alkalinity = 100ppm, Calcium = 220ppm.

I just added 10lbs. of 'Alkalinity Plus' and 16 ounces, of sodium bicarbonate, now the Ph only requires 30 drops of base demand reagent to achieve a 7.6 Ph, and the Total Alkalinity is now at 200ppm.

I don’t think that I am getting a false chlorine reading but am not really sure, thus I'm worried about adding more shock.

I plan as of the moment is to go and get more Ph rise.

Any one have comments or suggestions?

Thank You,

Froggy

[chem geek]

Froggy,

First of all, Chlor-Brite is Dichlor and you should never, never use Dichlor to shock a pool. For every 1 ppm Free Chlorine (FC) added by Dichlor, you also add 0.9 ppm to Cyanuric Acid (CYA). CYA reduces chlorine's effectiveness. It sounds like you got an algae bloom for green algae since that usually starts out with dull and then cloudy water before there is enough algae to become green. 2 pounds of Chlor-Brite (from Leslie's) in 15,000 gallons will increase the FC by 8.9 ppm and the CYA by 8 ppm.

You said you are using pucks which I assume are Trichlor pucks (it is also possible you have a special Cal-Hypo feeder, but I doubt it). With Trichlor, for every 1 ppm FC it also adds 0.6 ppm to CYA so if that has been your primary source of chlorine, I suspect your CYA level may be through the roof and over 100 ppm which is very bad, but would explain why the pool might be developing an algae bloom. Also remember that Trichlor pucks are highly acidic, especially after accounting for chlorine usage (which is also acidic) so that is how the pH got low as you need to regularly add chemicals to raise the pH when using Trichlor pucks. You need to test the pH regularly -- just looking at the water quality is not sufficient to know if the water chemistry is balanced. Do you know how many Trichlor pucks you went through in the 3 days between "good" readings and this current low pH situation? Something seems fishy here. Could anyone have accidentally added Muriatic Acid or Dry Acid to the pool?

I don't know which brand of Alkalinity Plus you are using since it's possible the "plus" means it is more like pH Up than just raising alkalinity, but if I assume this is just Sodium Bicarbonate (aka Sodium Hydrogen Carbonate) and is not Sodium Carbonate, then 3 pounds will raise the TA by only 14 ppm and will only raise the pH by a very small amount. If instead you used 3 pounds of pH Up (Sodium Carbonate), then this would raise the pH though if your pH were very low, you wouldn't notice it. For example, if I started with a pH of 7.5 and a TA of 100 and then added 10 3" Trichlor pucks to your pool and had the chlorine (37 ppm FC) get used up, then this would result in a pH of 6.6 and a TA of 75. If you then added 3 pounds of pH Up (Sodium Carbonate), you would end up with a pH of 6.84 and a TA of 97 which sounds roughly like what you may be seeing. If I use 10 pounds of pH Up (Sodium Carbonate) and start with a pH of 5.5 and a TA of 25, then I end up with a pH of 6.3 and a TA of 100. The good news in all of this is that you actually measured some TA since some people who use Trichlor and don't adjust the pH end up with a pH below 4.5 so that their TA test turns red immediately.

IF your pH is currently at 6.8, then to get to 7.5 would take 5.5 pounds of pH Up, but that would raise the TA level to 140. If you want to raise the pH without having the TA go up as much, you can use 20 Mule Team Borax instead and need to use about double the amount by weight as you would of pH Up. So adding 10.8 pounds of 20 Mule Team Borax would raise the pH from 6.8 to 7.5 and the TA would go from 100 to 123. If you want to raise the pH with no change in TA, then you can aerate the water to drive the excess carbon dioixde out, but for an indoor pool that can be tricky to do without having lots of spray and moisture all over the place. Another alternative similar to the Borax is to use Lye (Caustic Soda) where only 2.2 pounds would be needed (about 40% by weight of the amount of pH Up) though it needs to be pre-dissolved in a bucket of pool water and then slowly added over a return flow at the deep end as with most other chemical additions. IF your pH is currently at 6.3, then it will take almost 21 pounds of pH Up to get to a pH of 7.5, but the TA would end up at 256 -- even using Borax or Lye you would still end up with a TA of 182. I would just get the pH up to closer to 7.0 and then let natural aeration deal with getting the pH higher with no change in TA.

So first thing to do is to add either Borax or Lye (or pH Up and then deal with the higher TA later) to get the pH higher. Also, add chlorinating liquid to keep the FC up (and stop using the Trichlor pucks) -- how high depends on the CYA level, but I'd keep it at 20 ppm until the pool clears (this assumes your CYA level is at least at 50 ppm though it's probably higher) and you'll have to keep adding chlorine more than once a day since it will get used up fighting algae, especially initially -- though I talk about a false zero chlorine reading below. Then, get yourself a decent test kit such as that Taylor K-2006 or the TF100 test kit from tftestkits.com and test your CYA level. If it's over 50 ppm, then I suggest you do a partial drain and refill of the pool to dilute the water to reduce it and stop using Trichlor pucks as your source of chlorine. Instead, you should be using unscented bleach or chlorinating liquid and for automatic dosing you can use The Liquidator. You should not let the FC level drop back down until the following three things occur: 1) the pool is crystal clear, 2) you measure minimal (<= 1 ppm) FC drop overnight or over an 8 hour period (since this is an indoor pool not exposed to sunlight) and 3) you measure minimal (<= 0.5 ppm) Combined Chlorine (CC).

As for a false zero chlorine reading, if you are using a DPD chlorine test -- the one where you add 5 drops and it turns red if there's chlorine and you measure the intensity of the red -- then that will bleach out above 10 ppm FC having you think there is no chlorine when there's actually a lot. You can either use an OTO test -- which adds 5 drops and turns yellow and doesn't bleach out -- or even better is to use a FAS-DPD chlorine test that can accurately measure chlorine up to 50 ppm by counting drops (the test kits I mentioned above use this FAS-DPD test and the TF100 also comes with an OTO test as well for a quick chlorine check). If the chlorine level is above 10 ppm, then the pH test can be affected as one of the two indicators gets bleached out, but this usually makes one think the pH is higher than it is, not lower.

To keep algae from forming in the future, you need to maintain an FC level that is at least 7.5% of the CYA level. That's why it's much easier to maintain the pool with a lower CYA and for an indoor pool there is no reason to have the CYA higher than 20 or 30 ppm. You do want some CYA in an indoor pool in spite of what the industry says because you would be overdosing with chlorine if you didn't since the disinfecting chlorine concentration is based roughly on the ratio of FC to CYA and with no CYA it's very high. For example, 3 ppm FC with 30 ppm CYA is equivalent to about 0.1 ppm FC with no CYA. Also, I believe that keeping the disinfecting chlorine level lower leads to a slower formation of disinfection by-products (chloramines, trihalomethane, etc.) but if it's too low as with your pool that probably has very high CYA, then breakpoint is too slow so the buildup of monochloramine (measured as Combined Chlorine) can occur. The good test kits I mentioned will accurately measure both Free Chlorine and Combined Chlorine using a "count the drops" FAS-DPD chlorine test and they will also test for Total Alkalinity (TA), Calcium Hardness (CH) and Cyanuric Acid (CYA) with the TF100 kit testing CYA down to 20 ppm while the K-2006 tests down to 30 ppm.

Since this forum is more focussed on spas than pools, I suggest you check out TroubleFreePool.

Richard