Risks with high alkalinity?

[Rangeball]

One I got my high alk in line, it was time to add more water due to evaporation losses. This shot my alk right back up of course, since my fill water alk is 320 ppm It's a viscous cycle that seems to have no end, and I'm contemplating just ignoring alk and enjoying the pool.

PH is again at 8. Pool is crystal clear. I don't have a heater or SWG, and pool is IG vinyl. I don't use calcium, and haven't for a long time.

What am I risking if I let the alk stay high and just try to keep PH below 8 by using acid as needed?

[CarlD]

You may get some scaling.

Please look at Ben's method for lowering Alk. I think keeping pH that high is a bad idea--it drastically lowers chlorine's effectiveness.

Basically, you lower pH to 7.2 or less, which pulls down the alk, then you AERATE to raise the pH. Repeat the process until Alk is where you want it. Then use Borax to raise the pH to the desired level.

[Rangeball]

You may get some scaling.

I've not noticed any at all, but will keep an eye on it.

Please look at Ben's method for lowering Alk. I think keeping pH that high is a bad idea--it drastically lowers chlorine's effectiveness.

Basically, you lower pH to 7.2 or less, which pulls down the alk, then you AERATE to raise the pH. Repeat the process until Alk is where you want it. Then use Borax to raise the pH to the desired level.

I've looked at that so many times I think I can probably recite it I'm familiar with the process, have done it several times, and frankly am tired of doing it. With such a high starting Alk, by the time I get it down it's time to add more water and the whole process starts all over again.

The elevated PH and reduced chlorine effectiveness is my main concern, but in Ben's "run a high PH pool" page, I get the feeling I may actually be ok, provided I stay ahead of my pool. I'd just feel more comfortable doing so if I knew what the risks of high Alk were.

[chem geek]

There are two problems with high alkalinity and both can probably be addressed. The problem with scaling can be addressed by having a lower calcium hardness and by keeping the pH lower (but that will be hard due to the other problem with high alkalinity). The other problem is that you will be outgassing carbon dioxide until your pH is at a higher point which is pretty much what you've been seeing.

First of all, just out of curiosity, since you haven't seen any scaling (and don't have cloudy water), what is your Calcium Hardness (CH) level? One thing you can do to avoid even the potential of scaling is to lower CH significantly (unless it is already). If you are going to have a pH of 8.0 with the 320 ppm alkalinity, you could have your CH as low as 50 or even lower (staying in the range of 10-50 would be nice, but even 100 or more may not cause you problems).

As for the pH affecting chlorine effectiveness, that is true, but it doesn't have as much as an effect as you might think because the CYA acts somewhat like a chlorine buffer resisting changes to the chlorine level from pH. Specifically, the disinfecting chlorine (HOCl) level gets reduced by about 15% when you go from a pH of 7.5 to 8.0 (assuming a CYA level of 30 ppm) so that's not too bad and can be easily overcome by running slightly higher levels of chlorine. I suggest you just use Ben's Best Guess CYA chart and add about 20% to his numbers to adjust for your 8.0 pH (assuming your CYA is at least 30).

If you look at the following chart, CO2.png, you can see how higher alkalinity leads to more outgassing of carbon dioxide and that causes the pH to rise. Your levels are off the charts, but I calculate that at a pH of 8.0 and alkalinity of 320 the equivalent outgas rate (the left-hand side Y-axis) is about 10 which is usually pretty stable. You would probably have a hard time keeping your pH much below 7.8

Richard

[aquarium]

One thing you can do to avoid even the potential of scaling is to lower CH significantly (unless it is already).

How is that done?

[chem geek]

How is that done?

Unfortunately if the CH isn't already low then the only way to lower it would be a drain and refill. If the fill water is high in CH (we don't know that; we only know it's high in alkalinity), then there isn't a good solution. So you are right that I really need to know not only what the current CH is in the pool but also what the CH is in the fill water. My hope is that the CH in both are already low (which would explain why there's no scaling nor cloudiness).

If the fill water is high in CH, then it's an extra bad situation because any filling after evaporation will introduce even more calcium in the pool. Let's see what the numbers are for CH before panicking. I'm also very interested because there appears to be no evidence of scaling nor cloudiness in this situation so this could give an even higher "limit" to the saturation index for a real-world pool.

Richard

[chem geek]

I don't use calcium, and haven't for a long time.

Jeez, it would help if I read a post more thoroughly! Rangeball, I would still be interested to know what your calcium level is in your pool and, if you don't mind testing it, in your fill water as well (unless you recently refilled your pool). My guess is that the CH is rather low which is good in your case and explains why you aren't seeing scaling nor cloudiness. [EDIT] I just read Tom's (waterbear's) post which surmises you have high CH -- at any rate, now I'm really interested in your pool's CH reading. [END-EDIT]

Richard

[Rangeball]

Jeez, it would help if I read a post more thoroughly! Rangeball, I would still be interested to know what your calcium level is in your pool and, if you don't mind testing it, in your fill water as well (unless you recently refilled your pool). My guess is that the CH is rather low which is good in your case and explains why you aren't seeing scaling nor cloudiness.

Unfortunately, a guess is all I have to go with as well. I don't have the capability to test CH (wanted to order Ben's kit but was waiting for the issues to be resolved, having good luck with OTO kit so figured I'll put off a full kit until next season). I live in a small town, and our one pool store screwed me big time last season and I refuse to do any further business with them. Our fill water is supplied by our local municipality, I'll call them to see what their last water test shows.

In the meantime, I thought I had this issue resolved. Previously I had been aerating WHILE trying to lower PH, didn't work and I got nowhere. Now I lower PH then aerate, and alk was staying low at 130-40ish, PH holding steady. I added about 3" of fill water (ph 7.2 alk 320) last week before my youngest daughter had a swimming party, and after the party my PH was back up to 8. Looks like I'll have to attack it again, and it will probably be a normal part of my pool maintenance life as long as we have such high alk fill water...

[EDIT] I just read Tom's (waterbear's) post which surmises you have high CH -- at any rate, now I'm really interested in your pool's CH reading. [END-EDIT]

Richard

I thought waterbear = Evan?

[Rangeball]

Called City Hall and had them fax over the most recent drinking water quality test report. Didn't contain a reading for Calicum.

Called the Water plant directly, they don't test for calcium

Does the 5/6 way drop test kit at Walmart test CH? They have some there for $12, I was thinking about getting one to see where my CYA is now that I used 4 8oz tri-chlor sticks while I was gone for a few days.

[chem geek]

Called the Water plant directly, they don't test for calcium

Do they test for total hardness and is that in the report? I have a calculator that can approximate the calcium hardness based on the typical 4 to 1 Calcium to Magneisum ratio (typical well and ground water -- mountain spring water is closer to a ratio of 2.6 to 1).

The formula is Calcium Hardness (ppm CaCO3) = Total Hardness / 1.412 (for a ratio of 4 to 1 and other conversion factors)
[EDIT]Sorry for the wrong factor the first time[END-EDIT]

Richard