http://www.drsfostersmith.com/produc...fm?pcatid=4387
Above is one more. I do use the Seachem
ammonia Alerts (in the link above) in my tanks and filters. However, I would not recommend giving up the liquid tests. I depend on my liquid tests and the Ammonia Alert as a back up.
The pH alert, I'm afraid I wouldn't be able to distinguish the colors well enough to get an accurate reading. I haven't used them so I can't say for certain.
I've also used pH hand held meters. I got tired of replacing the batteries

Too, they are a bit pricey.
Ken