I started reading about keeping tropical fish weeks ago and decided to do a fishless cycle. I went to my local aquarium centre and the chap there told me I didn't need to do that I could use a biological supplement instead, and could start adding fish a few days after getting the tank. So......

Day 1 I filled the tank. (160L)
Day 3 I tested the water; PH 7.6, PHHR 8.2, Amonia 0.5, Nitrite and Nitrate 0.
Day 8 Added 10 neon tetras.
Day 10 Asked the centre about my readings and they suggested a 30% water change and to use the biological supplement for a further week.
Day 13 Added 3 platys and 1 dwarf guarami
Day 14 I tested the water; PH 7.6, Amonia 0.5, Nitrite 0.25 Nitrate 0

I am so confused as to whether I have cycled my tank, or is that just for fishless tanks?. What should I do now? I was going to do a 10% water change on Tuesday.

Also when I went to another centre yesterday to get the fish the boy there told me I should wash out the sponges in the filters, but then I thought I read somewhere that this contained benefical bacteria.

I would really appreciate any advice anyone can offer. Up to now I have just 'googled' my questions, but that is just making me more confused, so I thought I would ask some experts.

Thanks very much.