I have never bought test strips, but with the LIQUID TEST KITS you get all the booklets with colour charts and ittells you how much of each regent to put in the test tubes. Sumple and easy to use.
With the amonia one, you get the colour scale 0 (light green) - 6.1 (dark green/blue), the best level is obviously 0, the dnager level is considered 1.2mg. If you have a level of 1.2 + then there is another chart that you cross reference, Amonia along the bottom with pH at the side, the chart goes from green, through yellow to red. The higher the amonia and higher the pH the more toxic your water is to the fish.
EXAMPLE - When I hadmy amonia problem -
Amonia level = 2.4
pH = 7.6
Cross reference = green, now I assumed this was considered safe so I didn't do a water changer.
1 Day later
Amonia = 3.7
pH = 7.6
Cross reference = yellow, still not toxic but needs lowering
Of coarse this was all when I didn't know any better, that's when I got some advice. I did a 50% water change for 3 days.
Now that I have had my tank for a while and have at least a little expereince I do an immediate water if it gets any higher than 0. Although that doesn't seem to happen these days.
If your test shows in teh red I would go by what Oldman said and do a 70% change.
Also on your water changes, just to make them quicker for each 10 litres you are putting in boil 1 litre, this brings your bucket water to around the same temperature as your tank water. So what I do on my regular maintanence water changes, I fill my 6 buckets, I take out 1 litre and boil it, put it back into the bucket, I do this for all 6 buckets. Then I add the dechlorinater. Then I syphon out the tank water. Just makes the whole process a little quicker.
Mick