Fresh water is easier as you don't have to worry about making up the right salinity etc.
The first thing to do is look on your water company's website for hardness. It's usually on the same page as the water quality report. If you can't find it, tell us the name of the company and we'll see if we can find the page.
Fish have evolved in water with a certain amount of minerals and it is easier to keep fish which come from the same hardness as our tap water. Soft water fish kept in hard water develop calcium deposits in their kidneys; hard water fish kept in soft water suffer calcium deficiency. Both of these mean the fish won't live as long as they should.
Can you also tell us the dimensions of the tank, please. Tanks in the UK are often taller and narrower for the same volume than tanks in other countries.
Once we know if you need hard or soft water we can suggest colourful fish suitable for your tank.
