so for run times i could put on a digital timer, manual says i can disable the SWG inbuilt timer and use external, then i could say run for 4.5 hours at 100% , but running 5 hours it crept up i wonder will knocking off 30 minutes be the answer, i guess thats all i can do, or try different times at the 75% output
OK, sounds like the SWG and pump are sync'd for safety, so check that off the list. Excellent.
And you have a good handle on the rest. Just watch out for one thing that might mess you up. And you'll need to check your SWG manual to see if yours works like ours do here.
If you run at 100%, then this is a non-issue. The SWG will be producing 100% of the time, and lessening the runtime by 10 minutes will give you 10 minutes less chlorine. All good. But if you try 75%, that might not work that way.
When I set my SWG for 50%, it doesn't make 50% less chlorine all the time, it makes the same amount it always does, but for only 50% of the time. It'll produce for 5 minutes, then idle for 5, then repeat. So if I lessened my runtime by 5 minutes, say from 60 minutes to 55 minutes, then it wouldn't make any less chlorine, because it wouldn't have been making any anyway.
So you need to figure out if your SWG has an on/off schedule like that, like 75% on and 25% off, and then find out what the on/off frequency is. Say, at 75%, your SWG makes chlorine for 45 minutes each hour, and then it idles for 15 minutes. Well, if you reduce the runtime by 15 minutes, you won't actually be reducing the chlorine output, because it'll still make chlorine for 45 minutes.
If your SWG has a faster cycle, like many do, then this won't matter much. Or if your SWG can dial down production by 25%, but still make chlorine for the full hour, then this won't matter either.
Just something to be aware of and figure into your runtime trials...