Query for analytical chemists - dip stick for ammonia

Factual Questions
1

I’ve a query for analytical chemists about what mechanism might be used for a dip stick test of ammonia in aquarium water.

The clear strip has three pads (I cannot find a good picture.) The procedure is to remove a small amount of water in a tiny test tube, shake the strip in the water for thirty seconds and then compare the color of one pad to a chart.

I had a few good courses in analytical chemistry many decades ago. I’m guessing that two of the pads release something into the water that reacts with ammonia and cause a color change in the third pad. Would you conjecture what chemical reactions might be involved?

2

I don’t know, but it’s probably something that gives a specific color to amines. Off the top of my head, copper would be my best guess. Does it turn dark blue?

There may be better, more specific and less potentially toxic (to fishies anyway) indicators, but a copper amine complex is very visual.