I have had a Fluval Edge tank, found it quite awkward for these weekly maintenance and water changes, how do you find that tank?
Sorry, but, WCMM are more temperate fish, means they prefer cooler waters compared to guppies and platies, also, all these fish are schooling/shoaling fish, means better in groups of at least 5 +, 3 + is doable but imho more is better.
Know its something you probably don't want to hear but platy does not belong in that small tank really, 20 gallon long is minimum really