Over in this topic:
This disagrees with our standard practice of not mentioning anything about PH beyond keep it between 7.2 (7.5) and 7.8. So the question is: In which, if any, situations is it important to think about PH before shocking?

This adds one more complication to an idea (BBB) that is supposed to be simple. In fact, it must be simple or people will soon lose interest.

Factually, there really are some cases wherein people maintain their pools perfectly by throwing in pucks and going swimming......all season long. Granted, those are the lucky few and far between, but I personally wish I had that luxury and I would hazard that probably 90% of the people on the forum would, too.

I think our message has to be pointed at the lowest common denominator, the newbie, who needs to understand the function of chlorine, why he needs CYA, and other basic ideas that far too many of us assume are already understood. Read the threads.....they are not.

Additionally, it seems the side effects posted above would affect a very, very small percentage of users.

There is something to be said for covering all situations and we want to be as encompassing as possible but, in doing so, we frequently get mired down in the minutiae that drowns out our overall message of simplicity and ease.

When a new member posts numbers and states they have a green pool, if their Ph is already above 7.8 I tell them to lower the PH first. That's usually the only time though.

I think this sentence is the key.

I personally vote to not cater to the least common denominator and be accurate. Besides, pH is one of the important parameters that must be controlled. I don't think adding a line to "How to Shock" that says drop pH first is really over the top.

I wrote up the suggestion because of the actual observations in 4JawChuck's post, which wasn't the first time we've seen where shocking at too high a pH relative to the shock level led to issues (mostly metal staining and slow clearing of cloudy water). Lowering the pH prior to shocking is one extra step that can be recommended, not required. His example was extreme due to the very high shock levels, but the principle applies to more normal shock levels, especially if one doesn't have borates for additional pH buffering.

By the way, shocking is supposed to be an unusual event in the BBB system, so this addition isn't to anything regarding regular maintenance.

In this example lets review the "shock" situation and how it relates;

FC - 60
CYA - 100
PH - 8.3 or higher

The addition of the high level shock (done with Cal Hypo) raised the PH so high the FC was ineffectual until I brought the PH down (muriatic acid) to cure the bloom (which was instantaneous!), it really was amazing to see the cloud of green dissipate and "bleach out" as white precipitate that I could vacuum up with the krawler.

Since this was two days ago (I drained the rest of the water at FC of 50 to avoid anymore trouble) here are this evenings numbers;

FC - 12.5
TC - 12.5
CC - 0
PH - 7.5
CYA - 55
CH - 250
TA - 90 (minus the 18.15 correction factor for CYA = 71.85)

In the past two days I have added 4 - 0.5kg boxes of baking soda (to correct TA) and one 18kg tub of Calcium to give me these numbers.

This evening I have added another 3 - 0.5 kg boxes of baking soda and .75 litres of muriatic acid to correct the rising PH and boost my TA a little, I intend to check PH in the AM to see if it requires further correction. The past two days have been exceptionally hot and sunny here (34C+) so the FC has been dropping quickly.

I will say that PH is very important when the CYA is very high and you need to super shock for algae from my experience with this pool which is not typical, if there is anything to add in the "pool school" or "how to treat for algae" section maybe just a notation on how high CYA and low TA levels affect the shock effectiveness which Chem noted in my post.

It should also be noted that the drain and refill took the better part of 4 days during which I started out with CYA over 200 (likely 250), since I am on holidays I was here the entire time to witness what was going on and luckily could react when the bloom occurred (happened in about 2 hours). In hindsight I think if a person is going to take this long to refill and drain a pool keeping the pool in shock the entire time would be less stressful and better able to cope with the influx of fresh water (from rain and the tap).

I will say this, the pool has never been bluer or clearer and everyone has remarked on how nice it looks. I went for a swim this evening with the light on and I seem to have some particulates that are not being filtered out so I am not sure if I have ruined my sand filter (channeling) with all the backflushing to drop the water as I was filling. I did the "magic eraser" trick on the liner area above the water line (wow does that work well!) and some of it seems to be bits of eraser floating around.

Tomorrows project!

Besides the "off" readings that one gets with high levels of chlorine while shocking, I would like to add that clouding can be a real "confuser".

I keep my pH at 7.2 with sequestrants to keep the iron staining (not from water supply but from our silt and dust) at bay and to slowly release calcium scaling. If my pH is at or a little above 7.5 additions of bleach will always cloud the pool which may take a couple of days to clear unless I bring the pH back down to 7.2. With 21/7 filtering, using cellulose, just about the finest filtering one can reasonably accomplish, the water stays cloudy until MA is added. And I'm not even talking about unusually high pH here. Addition of MA, to bring the pH back down to 7.2 or a little lower, clears the clouds virtually instantly.

I can see how, under certain circumstance, this could confuse some people (and those trying to help them) about what the clouding issue is. It took me a while for the light to come on to realize why my bleach additions occasionally clouded the pool.

A couple of hours ago I added 182 oz 6% bleach. The pump is running and the Aquabot is running. Before the bleach addition I could see a speck on the bottom of deep end; now I can't see the bottom drain. When I test the pH, in a few minutes, and add needed MA, the pool will be clear as it can be in < 20 minutes. I do want to add that my bleach addition did not take the FC anywhere near the level to affect the pH testing.

I just wanted to add this to the discussion. My circumstances are a wee bit out of ordinary for a "perfectly" balanced pool but I wanted to illustrate that, at times, pH can certainly add to the confusion that may come up when dealing with any level of FC.

gg=alice

Thought I would write a follow up to this conversation as it related to my situation.

The shock level of chlorine has abated and I am now on a regular regimen of maintaining FC between 5-9ppm, I had to add a small amount of PH up to bring the PH back into range after the high 50ppm FC subsided when it hit around 15ppm or so. I backflushed the filter again yesterday and my TC immediately went to zero, I feel confident everything is sanitary and the yellowish/green gook that came out of the filter for five minutes was literally a "shocker".

My numbers tonight are;

Temp-29C
FC-7
TC-7
CC-0
PH-7.5
TA-100
CH-240
CYA-60

I lost FC quickly during the shocking phase but it took a long time to come down under a FC of 10. My CC stayed up there for quite some time until I flushed the filter and then quickly went to zero after, guess it was all trapped in there. No more chlorine smell from the pool and the skin sniff test after swimming yields no odor I can detect so I must be in the sweet spot, my TA and CH readings have stabilized to where they are now and have not budged so I have stopped testing them everyday.

The "clouding" I witnessed when the bloom occurred certainly precipitated when the PH was corrected and this led to a PH swing that I had to correct as the FC came down over a couple of days, I think the speed that having the correct PH for the FC level which clears a bloom is worth the PH swing if you ask me...being able to vacuum it up right away and flush it from the filter meant the water was clear within a few hours. I'm sure you could let it clear on its own as the FC came down so you wouldn't have to do anything to the PH but I am on holidays and staring at a cloudy pool for that length of time would have pee'd me off.

I am very happy with the stability of the pool now that I have a couple of "normal" days of regular maintenance under my belt, this won't cost much money to maintain as I lose less than 2ppm FC per day even with a high bather load. I am using Cal Hypo to maintain the FC, I am still dialing in this part of the setup but my numbers today appear to be bang on for the FC level which is the center of the range for my CYA level.

I need to spend more time getting the amount of Cal Hypo correct for the daily FC usage as even small amounts of it greatly affect the FC level, I can see why liquid bleach is so popular since being out a little won't change things much. I have six jugs of liquid 10% Purox waiting here that I might switch too since it affects PH less and I could just eyeball the amount I am putting in instead of dealing with very accurate Cal Hypo powder weighing to nail it.

I think I am over the steep learning curve part, moving into a new house at the same time as dealing with this skyhigh CYA level made it stressfull but we are in relax mode now and just enjoying the last few days of holidays seeing a sparkly clear blue pool every morning. It was a probably a good thing I learned this now instead of being oblivious to what can happen, I like being in control of the situation and knowing what to do plus having an assortment of chemicals on hand to deal with anything that might happen gives me piece of mind.

The funny thing that happened while I was dealing with this is the kids started taking an interest in the maintenance of the pool, I caught my 9 year old out there this morning pulling the cover and skimming the pool and putting in the krawler and turning off the pump to clear the baskets...he even remembered to shut down the heater while he was doing it. He even wanted to test the water to make sure it was OK until I reassured him we were ready to go since Dad had her dialed in.

I was a very impressed and proud father I can tell you that!