Hi Robert and welcome back! I finally completely recovered my strawberries since my month 'vacation' of total neglect except one pH adjustment, but including nutrient exhaustion when ignored for the last weeks.

One thing I noticed, but have data on from my records was the way my pH swung with my fertilizer recipe. I left it a pH 6.9 to 7, and then checked it and found it at 6.3 a month later, and only 2.8 liters per plant. From past performance I know what happened, the pH drops from 7 to about 5 if nothing is done, then it inches up, the way my recipe is.

If you have a similar thing going on which you easily could, behind your back on vacation it may have dipped to say 5.5 which could have done that. The tomato will love that and can handle the higher pH but Swish Chard (your 'Silverbeet' variety) would react badly. Also a few hot days and the tomato would live it but the Chard wouldn't, and you were still coming off summer. Last idea is that if it's not all hydroton, the roots might dry out and get damaged more easily. So a combo of the pH primarily with the heat might be the old one-two that took them out...That's what I'd look at, anyway.

Hey, something is always lurking out there. My first commercial sized strawberries after recovery and I left them on "just one more day, about 10, and went out for breakfact to get those bigh plump sweet babies for breakfast and found a strawberry slaughterhouse from either birds or squirrels all my breakfast gone with random scraps of heavenly red strawberry flesh scattered all over the leaves due to the sloppy gluttons. Down to the last berry, and just because I had the greed/perfection of "oh, wait just one more day", why do I always do that! Anyway, try the chard again now that it's cooling down - don't give up on them yet!