The best "cleanup" species is Yousiphonicus Gravelcleanerii....
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Also, your tank is overstocked right now, so I wouldn't even consider any more fish.
I laughed far to hard at that lol.
+2. Your fish will absolutely be fine not eating for a couple of days. I let my fish fast for an entire week when I go on vacation. Worst thing you can do is let a non fish keeper feed your fish while you're away. RTC idea....just don't do it
+3...Either skip weekend feedings (I fast my tanks at least once a week) or tell your grandma what she needs to do or just don't do it at all. They are your pets at the end of the day I don't care who thinks they are more right lol.
DO NOT buy an rtc...just...don't. To many out there as is that can't be homed..