I have had trouble with the nitrate bottles. I kept getting readings of 110+ which is off the charts and finally got pissed about doing water changes every other day . I got a new kit aquatic pharm. and this shows 20ppm on nitrates . I have the same Hagan master kit you are talking about and I do not care for it . The color charts are to hard to tell on some tests. especially ammonia . Hope it works better for you if you do decide on the master kit ... IMO, good luck