Start up questions -- min pH for heater safety

[anonapersona]

One of the contractors I am considering for pool renovation has sent me their start up procedures at my request.

I am concerned that he is not concerned about the massive use of acid during start up while circulating through my heater. The start up procedure says that when the pool is done filling to add 2 gallons of acid to every 5000 gallons of water and adjust CH to over 180ppm (will start with tap water at only 20 ppm CH). Then the pool is put on circulation 24/7. Days 3 and 4 they keep pH below 6.8 (no idea how far they might need to push it if they add acid only once a day). On day 5 they adjust pH to 7.2-7.4. On day 7 they go to 6 to 10 hours circulation time and re-install the pool cleaner.

They use sequesterant during start up and recommend using in thereafter, forever.

My heater is about 13 years old, I am not sure that it will withstand some tragically low pH. The heater manual does not give any limit on low pH, but says 7.4-7.6 is ideal but below 7.2 is marginal and 6.8 - 7.0 requires correction.

I realize that I have no understanding of what actually happens, chemically, to a pool during startup. I know that pH tends to rise, and lots of acid is needed to keep it in check, but I am stunned that these instructions do not mention any minimum pH level at all and that they have no concern about low pH going through my heater.

So, can we discuss this a bit? I am wondering if this is serious enough to delete this contractor from my list.

PS. They also say to adjust TA to below 70 ppm, which will be hard given that my tap water is 220 ppm.

 

[JasonLion]

The effects of low PH on a heater start around 6.8 and increase as the PH goes lower and the length of time involved increases. A plaster startup is only a couple of days, so it won't be disastrous, but it will have some effect on the heater. Ideally you should bypass the heater during the startup period, though that is often a hassle (unless you already have a bypass installed).

Using an acid start on freshly applied plaster is very common. The associated low PH levels are commonly allowed to circulate through heaters. Although some builders will bypass the heater, that is rare. A bicarb start, which does not lower PH, is considered better, but is not in wide use. You might want to talk to the contractor to see if they will consider using a bicarb startup.

Lowering the PH that much will dramatically lower the TA. Chances are that it will go below 70 when using that much acid.

 

[anonapersona]

I am studying the bicarb start and trying to understand the chemistry of it -- chemistry was never a strong suit for me, interesting that all my hobbies include it, and electricity.

As we will have to have the equipment pad reset as it has shifted and everything is tilted and the pumps hanging on the piping unsupported, I may be able to get them to create a bypass capability, built in or temporary. This particular contractor has said he's never had a problem with the heater but I have to wonder if he would even be aware if a problem surfaced some time later. Maybe just reduced lifespan or something.

Also, there are moss rocks used instead of tile around most of the pool, as well as flagstone tiles in a few places. I know these rocks are soft, won't such a low pH damage them also? Rocks extend into the water about 4" at normal water levels.

Next question... if I go with a quartz or pebble surface, is a bicarb startup that useful? Is it only for plaster finishes? Or are all pool surfaces the same in that regard?

 

[JasonLion]

The rock will be fine. Rock is more resilient than plaster or copper.

A bicarb startup is somewhat more complex to do than an acid start. The long term difference is the effect on the very top thin layer of plaster. An acid start is designed to wear off the top layer of plaster to minimize plaster dust. This tends to leave a slightly porous surface and just slightly thins the plaster. A bicarb start is designed to accelerate the curing of the top layer of plaster so it forms a more solid and less porous surface, which also maximizes plaster thickness and helps minimize plaster dust.

Both pebble and quartz surfaces get acid washed to full expose the pebbles/quartz. You might as well start doing that right from the start using an acid start.

 

[anonapersona]

Thanks. Looks like we will probably go with a pebble surface.