Your opinion is well appreciated.
The environment for guppies and marine fish are two different scenarios and complete different environments.
But the idea is awesome.
I was going to use a bucket, no fish. To test change of pH, and heat/cold.
Then later when tank arrives to test in the sump only. Still no fish. But tank is full of water, and indirectly its waiting for the environment to be spot on. Ph 8.7 max
Salinity would also be checked electronically. Occasionally the hardware will be checked by checking the tests manually
E.A.Levy