New Tank Care

Question
Hi,
Firstly let me say this looks like it is  a great resource to have for us aspiring Aquarium owners. so thank you for your time.

Now I recently purchased a small 13L tank for my daughter, Setup the tank and filtered it for a week added two goldfish and all was well then the water turned cloudy and two days later the goldfish died. i was advised this was due to new tank syndrome. So the tank was cleaned as was gravel and ornaments and again filled and filtered for a week and water treated with TatraAqua Aguasafe to remove chlorine and the like. So after a week i purchased 6 White Mountain minnows (was going for goldfish but they just seemed so much more interesting) and at the advice of pet store added Some API Stress Zyme to help with the cycling of the tank and all seems to be going well. this was 3 days ago. i was advised when changing water just do 15 - 20change, but how often should i do this? also what sort of plant life would you recommend putting into this tank? i think my next fish to go in in a few weeks will be something like a small catfish is this advisable?

Answer
You should to a 15-20 change every two weeks or every week if you want to really keep things clean. Either way usually works. A small cat fish is a good idea they eat uneaten food at the bottom and really keep things clean. You can put any plants you think look nice in the tank. Just remember they do grow quite tall,usually. I hope this helps.