Sandy,

When you add liquid chlorine or bleach to your pool, you are adding highly concentrated chlorine that will "super-shock" your pool in a local area as it mixes with the pool water. 6% bleach is over 60,000 ppm chlorine so even when it dilutes into 100 times the amount of pool water as the amount of chlorine you added, this is still 600 ppm. The SWCG has been measured by manufacturers to have around 80 ppm in the cell between the plates though I suspect that as one gets closer to the plate itself, the concentration is even higher. The only difference between adding the liquid chlorine or bleach manually vs. the SWCG is the rate at which this is done. The SWCG is more "continual" which probably makes it more efficient.

In both cases, however, only a local area gets super-chlorinated over a short period of time. So long as the algae is "mobile" in that it moves with the pool water, then circulation will eventually have that algae/water move through the central portion of the SWCG cell and get zapped. Manually adding chlorine would do the same thing, but you'd have to add it where the algae is located or would have to add a little chlorine almost continuously near a return to somewhat simulate what an SWCG was doing.

If the algae is stuck to a pool surface, then the SWCG system will do nothing to it. Manual dosing of liquid chlorine or bleach will kill the algae if applied where it is located. It appears that the hard-to-kill algae, which may be yellow/mustard algae, requires a high concentration of chlorine over an extended period of time, but due to CYA levels it turns out that the Free Chlorine level would only have to be 2 ppm to kill this algae if there were no CYA (at pH 7.5). It's the presence of CYA that reduces chlorine effectiveness and while regular green algae requires very little actual chlorine to die (perhaps 0.6 ppm FC if no CYA), this yellow/mustard algae requires more.

Of course, there's nothing like an experiment to verify a theory so I see nothing wrong with your running the SWCG while you are super-chlorinating. The efficiency of your SWCG will be a little lower (due to the higher chlorine concentration), but that's all. Of course, if the SWCG was able to zap this algae in the first place, then we wouldn't be seeing it.

In fact, has anyone seen the hard-to-kill mustard/yellow algae when using an SWCG system? This thread has several users of this forum reporting this hard-to-kill algae, but I can't tell if any of them have SWCG systems.

Richard