Adding nitrate

[stygian7]

I'm trying to learn how to control my algae problem by adjusting the nutrient levels. I've been adding KNO3 over the past couple of weeks. I'm shooting for a nitrate level of 5-10ppm. Do I need to concern myself with nitrite levels-can the plants use nitrite as well as nitrate? After I add the nitrate, the level goes up to about 5 ppm, then a 4 or 5 hours later it's below what I can read. I know that I'm not adding 5 ppm all at once. It should be about 1 ppm with each addition. Unfortunately, I'm colorblind so the scale is difficult for me to read. I'm using a seachem nitrate test. Is there a more visually friendly test out there, or even better-a digital meter?
For background info, just in case:
I have CO2 run by a controller, so there should be plenty of usable carbon. Lighting is 3-175 watt metal halides and the substrate is fluorite with a little bit of onyx sand mixed in. The water is set up on a constant drip system that changes about 35 gallons/day (125 gal. tank). Feeding mostly bloodworms right now to 14 discus and 4 or 5 tetras.

[ChloroPhil]

Plants will use Nitrogen in all forms in preferrence of Ammonium (NH4+), Ammonia (NH3-), Nitrite (NO2), and Nitrate (NO3). If you're finding that soon after you add Nitrate that the level has dropped significantly then your plants are most likely deficient and are sucking it up to store. Try adding it more frequently.