Actually, since most of us are using hobbiest grade test kits, a Nitrate level between 20-40ppm is generally considered good. Reason being that hobby grade Nitrate kits are often highly inaccurate below 20ppm, especially if they haven't been calibrated against a reference solution. Often test results below 20ppm can actually end up being 0ppm and the cause of algae problems.
Generally you're going to want your Phosphate levels between 1-2ppm for every 20ppm of Nitrate. This is just a starting place and you can play with the ratio some as needed. Many have found that they need to dose the Phosphates a bit higher to get rid of Green Spot Algae.
For Potassium, you'd want to dose between 10-20ppm per week. There isn't a hobbiest kit for this nutrient, so you need to rely on dosing and your plants to show you if there's a deficiency. Luckily it's nearly impossible to overdose, so you just need to ensure that you're dosing enough.
That being said, the easiest method of dosing is probably EI (Estimative Index). Basically you dose enough each week to ensure that you never risk a nutrient bottoming out, and then do a 50% water change at the end of the week to reset your parms and ensure that the levels don't get too high.
Also just for reference, you pH and KH relationship appears to be out of wack. As I recall from another thread you aren't injecting CO2, but your readings indicate a deadly amount of CO2. In a non CO2 injected tank the CO2 levels are only about 3ppm, which means you won't be able to rely on pH and KH readings from your tank to determine your CO2 levels if you decide to start injecting at some point. You'd either need to use an alternative method of measuring CO2 or a CO2 drop checker.
