Are you talking items that stay in your tank and you can monitor? I'd say the cheaper route is a Hanna Instruments Testers
for pH and TDS
. I would also suggest a Refractometer
. As for the calcium, you can just buy a Ca
testing kit. I know there are other "active" monitoring devices, but I don't own one and can't remember the site I saw them. I believe, once you get the hang of taking care of your tank, you won't need those other things. I would suggest, just test your water, learn how your tank works and keep up with regular PWCs.