The reagent comes in a concentrated mixture. The unit itself came with a 250ml bottle, which you add 1L of RODI water to. The first mixture got me through 13 days: To put this in perspective though, I was calibrating pumps trying to figure out how to set it up, and I had it going every hour for the first 3 days. Then I switched it to every 2 hours. I just made a second mixture this past weekend, so I'll see how far this batch gets me. Likely 15-20 days at every 2 hours. 1L concentrated reagent is currently $29.99, 4L is $110.00 So if Im testing every 2 hours, lets say I get at least 15 days, then realistically I could get 60 days out of a 1L. If I move to testing every 4 hours, then 120 days per 1L. I'm not sure what the best number for testing is. I like being able to see what the tank is doing through out the day. Testing every three hours could get me to about 90 days, and then the 4L bottle would get me through the year. on another note, I got the shroom out of its cave and back out in the open. couple of better photos. Hopefully it takes to the new location!