Can R-007 be used to neutralize high FC before performing the pH test to get an accurate reading or will this further interfere with the chemistry?
chem geek said:No, I would leave the pH alone. You don't need it higher to kill algae. And odds are that his pH reading may be correct. When the pH reads falsely high, it's false reading is quite high. It won't falsely read a lower reading. If you get a reading of 7.5 or below, odds are it's a correct reading. It's when it looks like 7.8 or 8.0 or higher that it may not be that high. Remember what Taylor says about this process:
The part that Taylor is missing is that the "quickly and completely" occurs when there is no CYA in the water. With CYA in the water it appears that this conversion process takes longer, perhaps 30 seconds or a minute, depending on the FC/CYA ratio. We have just been conservative and simplistic about high chlorine interfering with pH just in case the CYA is low or people don't take a reading quickly. Also, adding a hypochlorite source of chlorine in large quantities WILL raise the pH significantly, especially when CYA is present and borates are not used and if the TA isn't high.FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purple color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.
When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.
JasonLion said:You can't win with sodium thiosulfate and the PH test. Adding enough to have any meaningful effect on the FC level will throw off the PH reading. If you absolutely must have PH readings when FC levels are high, you will need a completely different approach. However, there really is hardly any situation that comes up when you are following our recommendations where you need to measure PH at high FC levels.
The PH test gets less and less precise as the FC level goes from 10 to about 18. Somewhere between an FC of 18 and 21 the results switch to being completely unusable as the indicator dye gets chemically converted to a different compound by the chlorine.
If the pH is correct, or slightly at the low end, there should be no problem. While bleach is alkaline, after it breaks down the net pH change is very small.JesseWV said:So ideally pH levels should be adjusted before shocking. Obviously if you've already added shock level chlorine it's too late. Should pH really be ignored until after the shock process is over?
This bothers me because one of the criteria for completing the shock process is "the water is clear." I can see this being a problem for someone with a high CSI. With improper pH the water may never become clear due to calcium precipitates. I suppose the filter will eventually get it but that could take much longer than necessary if the pH was in the proper range in the first place, correct?
JasonLion said:You can't win with sodium thiosulfate and the PH test. Adding enough to have any meaningful effect on the FC level will throw off the PH reading. If you absolutely must have PH readings when FC levels are high, you will need a completely different approach. However, there really is hardly any situation that comes up when you are following our recommendations where you need to measure PH at high FC levels.
The PH test gets less and less precise as the FC level goes from 10 to about 18. Somewhere between an FC of 18 and 21 the results switch to being completely unusable as the indicator dye gets chemically converted to a different compound by the chlorine.