This probably seems like an elementary question.....but ammonia is present in my tank, why?

It has been 0 for months, now it's .25 to .5 ppm. I did a 15% water change and then 2 days later did a 20% change. No effect. I can't change water much faster because the water going in is 8.4 pH and the tank water is 7.6. It takes the driftwood a while to lower the pH of the new water.

No new fish, new equipment, or dead fish. Feeding is the same, which is already light.

Huh?

Also, what is the best way to see the true color in the test tube? I already have a hard time reading subtle color differences so these tests are a challenge. I've heard different things, like look at it under natural sunlight, or only under fluorescent lights. Hold it against a white background, hold it above a white background, look straight down into the tube over a white background....etc. For the API ammonia test it should be yellow. Any shade of green indicates ammonia, but it seems to change color depending on which "technique" I use for examining it.

Ugh.

Z

Different florescent lights could make colors look more purple or more yellow. Just go outside with the color swatches, your test tube, and look at them. If you want to be super accurate look at them with a white bg / sheet of paper.

did you recently clean your filter? Lack of bacteria maybe?

Plenty of bacteria, and no stirring like that. It's looks cloudy today but haven't tested....