I have no idea what it says.
Looks like between 0.5 ppm to 1.0 ppm, but closer to 1.0 ppm.
I'd go with 1ppm.
1 ppm, and that is very bad news. 75% water change, or 2 back to back 50% water changes with a little rest period in between, if you have fish in that tank. Consider salt to counteract the toxic effects of nitrite, again, if there are fish involved.
How much salt? It's a 20 gallon tank with one guppy in it and that's all.
I believe that would be 2 teaspoonful total, pre-dissolved in tank water. Then add the solution. Very little salt, should have no stressful effects or anything. Someone correct me if I'm mistaken...
How long has this tank been set up? What are your other readings? I agree that you'll want to do a large water change right away to get that nitrite down as close to 0 as possible. I have read salt will help with possible nitrite poisoning but not sure on the measurement.
Unfortunately, I had to leave the office where I work (that's where this tank is) and I didn't get a chance to do a water change and couldn't find out how much salt to add, but I'll be back as soon as I can be tomorrow and I'll do a water change then. I don't feel that I can really take good enough care of any fish in this tank while the tank is cycling, and I want all pet fish to be in cycled tanks, so I'm advocating for bringing him to a small business fish store I have picked out that seems reliable and then getting all new fish once the tank is cycled. It's been set up for about a month. The other readings from tonight: 7/17/17 Nitrate 15 ppm Nitrite about .8 ppm? Ammonia 0 ppm High range pH 8.0
Again, the recommended dose for salt in nitrite toxicity is one teaspoonful for 10 gallons. Two teaspoonful for your 20 gallon. Dissolve it in a small container of tank water. Do this after your large water changes. You will want to replace however much salt you remove in future water changes, until the nitrites are permanently gone. Then you can remove the salt over time with ordinary water changes. Good luck!
I meant I couldn't find how much salt to add until after I had already left.