Pool size 18k gallons. Jandy Aquapure700 is 3 yrs old. Unit was on 100%.
Now shocking to kill Black algae but owner has suspicions unit is not working. I thought that since I saw fine bubbles fom returns that it was working but unit is turned off and bubbles continue.
Day before we arrived here, pool co measured FC 1.5 at 5 PM and pH 7.6. Next morning at 11 AM I tested FC trace and pH 8.2+ with CYA 30.

Owner may need to consider a properly sized SWG, or adding a second unit. I have no idea of costs. Does anyone have experiance on relative costs?

I'd try catching a sample from the return and test the FC level of it. If it's high, the SWG is working. But it will never generate enough to shock the pool, not if there's algae blooming. Running it full throttle probably burnt out the element. Or will, soon.

looking at ebay costs i'd probably recommend replacing it for a bigger unit rather than adding second one.

looks like it's been running on the edge, and either started to die, or the pool got algae so it can't cope anymore

What kind power is it drawing? Amps and volts?

Nothing you have said indicates any problems with the SWG. Of course, there isn't anything that proves that it is working either.

With CYA at 30 I wouldn't expect anything but the most oversized SWG to be able to keep up. I would wait for more information before considering doing anything with the SWG. The water is clearly not properly balanced, and that should be dealt with before anything else is considered.

Thanks for all replies. Forgot to sample at return and away before shocking. Owner learning to test with TF-100. Will wait to see on SWG after FC to 5 or 10 when sample at return may show difference. How much difference to look for?

The FC increase you should see depends on the size of the SWG relative to the rate of water flow. In most setups it will be several PPM. If the percentage setting and pump run time are both setup correctly for routine usage it should be about 150/<percentage setting> ppm of chlorine increase over the level in the pool.

I so appreciate this help.
Next question, there are pits in the plaster where the BA lurks. We are resting trichlor tab on BA for 10 min, then scrubbing with SS brush. BA is fading but some left in pit.
Thinking to continue shock hoping it goes away, then fill pit with two part pool epoxy.
Will this wlrk,or is it a bad idea?

Update. We did cure the Black algae, but the SWG seems to have died anyhow. I cannot go there to check on it, and the owner hasn't been there either. The pool company has put a puck into the skimmer (not a great idea) and at least a week has gone by now. I have advised the owner to get a floater and fill it to the top with pucks, and let pool co come and shock it weekly since CH is reasonable at 290 last I measured.. Last test had CYA at 60 so they have that luxury. I assume that we can control the pool while the pool company dithers.

Back to the other question about sizing, it seems to me that this is the time to right-size that SWG. No way to know if the board is going to last much longer, some of the digits on the SWG% readout were not legible, it is not that protected from the sun and salt air.

Any advice? If I get a chance I will try to find the answer to the power question, but unless hubby decides to go for a short trip without me, I doubt that will get done.

I tend to think the pool co are idiots in how that pool has been maintained, and they installed the undersized unit post Ike (so maybe supplies were limited, in their defense) but I don't really trust them. The owner is not there enough to manage it, the guests don't care to help it seems.