Don't worry about it; the fish will be fed twice a week, not every day, so the water quality shouldn't suffer. Are you leaving the food already measured out and hiding the rest away?. However well-meaning your 'minder' may be, the sight of a tub of food might just be too tempting. Just do a water change a day or two before you leave, just so you know everything's working fine after being switched back on before you go. Enjoy your hols.
you may need to instruct whoever is doing the feeding how to top up water too, as if its warm then there might be a considerable amount lost from evaporation
you may need to instruct whoever is doing the feeding how to top up water too, as if its warm then there might be a considerable amount lost from evaporation
That's a good point; try to fill several large plastic bottles with dechlorinated water and leave them in a cupboard somewhere (out of the light). Mark a level on the tank and tell your helper that if it falls to that point, to empty the bottled water in to bring it back up to the usual level.