Oliver, thanks for the new information on Nitrate's...how high is too high. It answered one of my most asked questions and is the best answer as to why my fish were dying.

Your statement on trying to determine where the level was once it exceeded 40 ppm was right on...mine were pushing 200 ppm. I did it your way "if you dilute the fish tank water in the test tube by a ratio of 4:1 with distilled water (4 parts total, 3 distilled, 1 FT water) then you would multiply the measured results by 4." to find out what my Nitrate level was at.

Now let me ask you this, I just took my FT water and add 2 drop instead of 10 drops to test the water. That's 20% testing solution into the FT water, than multiplied the reading by 5 to bring it back up to the 100% range. It seems to me that the read out is the same...which was way too high. I backed off on fish food and started doing water exchanges to get my Nitrate level back down to around 100 ppm.

I also think that the high Nitrate level had a negative affect on my plants.