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Early on (during cycle) monitor Ammonia, Nitrites, and Nitrates. After the tank cycles you'll want to monitor pH, Nitrates, and Phosphates. If you used base rock (particularly limestone) it will leach trapped nutrients and cause algae (bubble, GHA, etc.). Use GFO or another method to export these. During this time, stick with soft corals, fish, and a CUC. Once you've got an established tank, nitrates and phosphates should remain in check depending on feeding and tank maintenance. As the tank ages and you get into LPS/SPS, it is imperative to monitor Alk, Cal, & Mag. Increased water changes may become necessary to keep up with the usage of these nutrients. Dosing is another option.
This is my experience. Hope its is helpful.