It really worked, can't believe that my silly white lie has kept him happy for all that time. Just make sure you visit 'mummy and daddy' in between to say hello
No downsides to tropical really. Only the small cost for a small heater, but for that size you can get one for £10-£15 easily. You really have much more options with tropical. And as said, the cycling will go much faster as you can bang up the temperature to help the bacteria grow.
I bought a heater and have told my son that it takes a very long time to heat the water up, hence why we need to wait a few weeks.
I started my fishless cycle Fri.