AquaJamieB Posted January 16, 2004 Share Posted January 16, 2004 I am still cycling my 20L, and am using the Fastest testers. My question is, during the cycle, why only use 5 ml of tank water and the rest fresh in the tube, but after established, fill the tube up with all tank water? What makes the difference? Link to comment
Tempest Posted January 16, 2004 Share Posted January 16, 2004 No clue. I don't like the Fastest stuff and do not use their tests. I can't think of why you'd add fresh water to a nitrite test. Reread the directions, maybe you just made a goof. Link to comment
mtglore Posted January 16, 2004 Share Posted January 16, 2004 Well, I do use and like the FasTest kits. I have never used their nitrate kit, however. When using their other tests, though, no freshwater is involved whatsoever. For calcium and alkalinity, for example, you fill the 5ml tube COMPLETELY with tank water and then pour into a larger tube for mixing with reagents. The 5ml tube is just for collecting the correct amount of test water. Perhaps I read your post incorrectly, or maybe you are finding the directions a bit confusing. OR, because I am entirely inexperienced with the FasTesT nitrate kit, maybe I have no idea what I'm talking about... Link to comment
faust9 Posted January 16, 2004 Share Posted January 16, 2004 Dilluting the sample allows one to use the same test kit as both a high range (during the cycle) test kit and a low range (after the cycle) test kit. The fresh water dillutes the sample lowering the total concentration by some ratio (10:1 if I recall correctly for this test kit) which raises the effective measuring range of the kit by the same ratio. For instance, if your tank had 5 ppm nitrite and your test kit only read up to 1 ppm you wouldn't be able to tell what the actual concentration of nitrites was other than <1 ppm. A little chemistry for ya: the concentration equation is: Cf(Vi+Va)=CiVi+CaVa where: Cf is final concentration Ci is initial concentration Ca is added concentration Vi is initial volume Va is final volume You can see that (using a little algebra): Cf=(CiVi+CaVa)/(Vi+Va) Thus if we make up some numbers for illustrative purposes: Ci=5ppm Vi=5mL Ca=0ppm Va=50mL Cf=(5ppm*5mL+0ppm+5mL)/(5mL+50mL) Cf=.45ppm This .45ppm will register right about the middle of the scale. Now multiply the .45ppm*10 you get 4.5ppm which is close the the actual 5ppm. If I wanted to (or if you want to for that matter) I could find the exact ratio using the above which would yield 5ppm measured for a 5ppm actual, but I'm lazy (requires calculus or trial and error to find exact ratio) but I think you can see my point with what I've shown above. Anyway, Good luck, and have fun... Link to comment
AquaJamieB Posted January 16, 2004 Author Share Posted January 16, 2004 How can i have fun with all that math invovled? Just kidding, thanks for the great info. Link to comment
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