Types of non-aggressive fish

Question
Hello Jon and it's great to have a friendly invite to ask questions!

Here is mine.  I have set up one of our tanks, a smaller one, 29 gallons, once again.  This time I'd like to try tropical fish in it. I am currently going to begin cycling it using no fish, but ammonia, etc. and will be doing readings, etc. as the days go by.  

What I need to know, as I'm going nuts reading stuff on the internet about various types of fish and so many different opinions, is can I keep guppies with platys and cory catfish.  I know these sound 'common' but to me who only own fancy goldfish & male Bettas, sound colourful and non-aggressive.  I was going to go for Tetras but heard they like soft water.  

Our water is hard because it leaves mineral deposits if any splash droplets on the window or e.g. in the bathtub.
I'd like hardy fish, 3 different types, colourful and not prone to fin nipping/aggression.

Our tank is 30" long, 12" wide and 18" deep.  I will be putting silk plants in and leaving the lighting to natural light coming in (no top lighting on tank).  We have all of our fish like this and they thrive.  I've heard cory catfish don't like bright lighting anyway.

On some forum, somebody said their platys are aggressive to the guppies and guppies have a tendency to 'fin-nip'.  I thought I had everything sorted out as far as fish go, now I feel back to square one again.  Please unclutter my brain, hee hee.

Thanks so much!
Paula  

Answer
Well Paula, the combination of fish you mentioned will go together great. I've never seen an aggressive platy as I have them myself. You can get tetras that are quite harder though. Scissor tail rasboras are perfect, I have 3. If you are looking for a good color combination of community fish, I would tell you to look into scissortail rasboras, dwarf gouramis, glofish, zebra danios, etc. Most fish are captive bred and are very adaptable to ph levels and somewhat hardness no matter where they are bred. Even angelfish will combine with the types of fish I mentioned to make a great combination of aquarium fish, given the angelfish aren't too big as they will eat live fish that may fit into their mouth once they're bigger. If your water is in fact extremely hard, than you may want to consider cichlids that are naturally inhabitants of harder water. The choice is yours! Let me know what you decide. And as always if you have anyother questions or concerns or comments, I'm here. Good luck.