I agree with Shawnie when it comes to not using it as your ONLY source. I have them in both my tanks and they make me feel more at ease as well. I test
pH every 5 days...I test ammonia, nitrites, nitrates once a month. (my tank is 8 years old, and I haven't added fish in 5 years). Should you add more stock or make significant changes in your tank then I would test more. (or if it's a new tank I would test more also)
Too, on the ALERTS that I have it says they are good for 1 year. I feel more comfortable changing them every 6 months. I tested one a long time ago by holding the ALERT over an ammonia bottle and it actually worked and changed colors. I like them.