dolphin said:
for instance, i read somewhere ( i could give you the link) that below 7.5 pH, the Hypochlorite acid is less dominate but the Hypoclorous acid is. The latter is not as effective.
You really need to look at the links I put in my posts that I write for you (e.g.
this post I referenced in
this post above). It answers your questions. Below pH 7.5, there is more hypochlorous acid than hypochlorite ion, so you got that part right, but you said "the latter is not as effective" with "the latter" being the hypochlorous acid (in what you wrote) and that is incorrect. It is hypochlorous acid that is the effective disinfectant. However, as my links showed you, when CYA is in the water, the reduction in the amount of hypochlorous acid is FAR less as the pH rises and it is also less of an increase when the pH drops.
dolphin said:
At 7.5, both are present and equal in the water.
also, wouldn't the pH lower, if more dirt ( bacteria laden dirt) enters the water? Since the micro organism ( not sure about algae) are ' - ' negatively charged?
if the water is more negatively charged would that indicate a lower pH?
pH and negative charges have nothing to do with each other in terms of the surface of bacterial cells having a negative charge. Bacteria themselves are NOT net negative. Their negative surface charge is balanced by a positive internal charge -- the cell surface molecules are polar. They do not have a net charge, but a charge separation. You are confusing the fact that hypochlorite ion is less effective because it is negatively charged so is repelled somewhat from the surface of cells while hypochlorous acid is neutral and looks very much like water so enters cells more readily.
dolphin said:
And a domino effect could start right? the lower the pH the less effective the CL and of course, the lower the effectiveness , the more the presence of negativly charged organisms ( the stuff mentioned)
so it would be important to maintain a close to ideal pH at all times ?
The lower the pH the MORE effective the chlorine, though not by that much when CYA is present. Maintaining a close to ideal pH is not that relevant in terms of chlorine effectiveness -- again, going from 7.5 to 8.0 only has the active chlorine (hypochlorous acid) concentration drop by 15% when CYA is present compared to 50% when CYA is not present (though when CYA is not present, the active chlorine level is way too high). So again, stop reading other sources that are either wrong or half-true.
dolphin said:
And of course, maintain, as you mentioned, a CYA of 30 ~ 50 @ 4 to 7 FC mentioned earlier.
another noteworthy thing to mention from this website: below 7.5 the hypochlorous Acid ( the weaker of the 2 ) is more prevelent so when you test for FC's, youll get a high reading; falsly believing you have all the killing power of Hypochlorite Acid
this makes for good reading:
http://blog.myronlmeters.com/tag/free-chlorine/.
As for testing for FC, it not only tests hypochlorous acid and hypochlorite ion, but even more importantly it is mostly testing all the chlorine attached to CYA and that is the least effective form of chlorine of all of these. This is why the Chlorine/CYA table is so critically important to follow and is MUCH more important than worrying about whether the pH is 7.2 or 7.8 or 7.5.
As for that link you provided, there is also a lot of misinformation about ORP, so again I implore you to stop reading all the incorrect or half-correct or incomplete information you will find on the Internet. For example, the "unknown chlorine species" in Figure 2 in that link likely reacts with the dye and is probably chlorine that has been released from CYA. If you have specific questions, then ask the here, but please stop copying or referring to all the other information since we will spend all our time correcting it all when this information has been discussed ad nauseam many times on this forum. The Pool School gives you the net result and you can search this forum for accurate information from the mods and significant contributors.