> I'm not sure if the appropriate direct sensors actually exist at low cost In some cases the sensors do not exists, at least not at low cost. Sensor life is

> I'm not sure if the appropriate direct sensors actually exist at low cost In some cases the sensors do not exists, at least not at low cost. Sensor life is also a problem. Part of my plan was to have some parts that used long-lasting color-changing sensors with color detectors to read the colors, and the system would prompt me to change them occasionally. SeaChem's Ammonia Alert is an example. I could not find a cheap electronic sensor that would test ammonia levels in water that would work in my system. Another part of my plan was to have replaceable sensors (if possible) so a fish breeder or reseller with 100 tanks could move a few hang-on-back water testers to one tank and see if one of them has a reading that disagrees with the majority, and swap or replace cheap sensors as required. Replaceable sensors are hard to waterproof, but it is possible. I do not know if we can hobbyist-proof replaceable waterproof sensors. The first version would probably have to be disposable. > I do think you could basically make it automatically read physical dip-in test strips The issue with automatically using dip-in test sticks is you do should not return the water from the dip-in test strip to the tank. You end up with a significant amount of wastewater and used test strips that the customer must empty, and then they must refill the test strips that are not supposed to be exposed to air or water. That kills the system's marketability.