Hiya, I have a 30L (approx 8gallon) tank and a Haile HL-BT-200 filter.
To be fair I'm not sure what additives were put in. My friend helped with all of that and gave me it in unmarked bottles (from the store to save me on the set up). She said one was a prime and the other a stabiliser. She also did the pH test and said it was fine before I put the fish in. I will be buying my own test kits etc but haven't as yet as the set up (let alone the fish) cost me a pretty penny and she is happy to so all that for me until I get that sorted next week.
I have tropical flakes for my platy's and high grade betta pellets for my betta. Current plan is feed every 2 days, as much as they can consume in 2mins or so I have been told. I'm sure we will fall into a routine as I get to know them better
And part of the reason I came on here was to check how often I need to change their water

The tank instructions state weekly with a magnetic brush and only a 1/3 change monthly. But everyone on here seems to be saying every few days. So I guess it will be every few days.
I will get some pics soon. He is a beautiful dragon betta in silver, blue and red. My daughter picked him out and is very pleased with herself.
Thanks for the advice. I will put a couple of coffee mugs in the bottom until I can go and get some ornaments for him next week
Water is at 25C