The digital era is here
You can get nitrate/ammonia/calcium ion selective electrodes. I think also potassium, fluoride and chloride there may be more.
Big money. Limited lifespan. Depends on your needs. If you own one tank, don't bother. (Depends on stock value and data requirements)
Data loggers and associated electrodes are expensive.
(I'm looking for absolute accuracy and precision)
To upgrade from a typical test kit, look at photometry, lots of money but accurate, if you want digital data, ion electrodes or lab grade bench meters.