You can find an inexpensive digital PH monitor, but for Ammonia, Nitrate, and Nitrite the only electronic testers I have seen for saltwater are "colorimeters" and they are very expensive I believe they start at about $700 for a multitest colorimeter and go up, I have seen single test colorimeters for about $200 each. Then on top of the colorimeter you still need reagents are not all that cheap either most are in the range of about $40 for each reagent some are more or less depending on which component you are looking for. You can test for just about every element in a saltwater tank with a colorimeter if you want to spend the money but just for the basic tests you are looking at $800-$1000 to get started.