Unhappy Platy Fish, Can you help me understand water levels?

[Gillian]

Hello,

I'm new to fish keeping. I bought my aquarium in December and got my Platy's in January.

I have a 17lt tank with 6 small platys, 2 males and 4 females. It's cold water, there's a filter and I do a 20% water change every week. I feed a small amount of flakes one a day. ( After reading this forum I have become aware my tank may be too small and I'm going to invest in a bigger one once I've saved up).

The problem is, one male has been really unhappy, hanging around the top of the tank in the corners with fins all tucked in. He perks up at feeding time and chases everyone away from where he's feeding.

After googling I bought some test strips to test my water levels, but I have no idea what they mean and how I can fix my water.
GH -0
KH -0
PH -7
NO2 -0
NO3 -40-80

If anyone could help me understand these readings and how I can make my fish better, I'd really appreciate it.

Many Thanks

 

[Autumnsky]

There is a wealth of information in the article link in my signature. More links after getting to that one for even more info.

Start with all of that after a good pwc of say 30%. Then check the levels and see what you have.

You say cold water, what is the tamp of the tank running right now?