I am going on vacation for about 18 days. My grandma is going to be at our house watching the dogs and the fish tanks. I have a couple tanks that I use fertilizers on a regular schedule. Can I skip the dosing to make it easier for my grandma? Or should I pre-measure out ferts and have her throw them in the tank on the days they need to be? There will not be a weekly water change of 50% either. Should I just turn down the lights so it is not so bright and try to put the tanks on autopilot? I need help.
Unless you have an experienced tank keeper watch your tanks, it's best to keep things simple. Having someone feed the fish is dangerous at best. I'd suggest you measure out the food and let the grandma do that only. Measure out about half the normal amount, so grannie doesn't feed too much.
There are several things you can do: A couple of weeks prior, start feeding the fish a little more. A couple of days before leaving, stop feeding and give grannie her instructions. Tropical fish can go a couple of weeks without food with no problems.
The day before you leave, do a larger than normal water change and vacuum well if possible. Changing out half the tank volume isn't too much.
I don't do much else when I'm gone, but the most I've ever left my tanks is 2 weeks and there were no problems.
If grannie "has both oars in the water", your tanks should be fine. Just don't ask her to do too much. If possible, it wouldn't hurt to give her the number of the local fish store, if a good one is near. She may not be able to contact you right away if something should happen.