Thank you so much for your reply! Since I have some experience with freshwater tanks, I'm not a complete beginner. I use liquid water tests, which I believe should be accurate. I just ran a fresh test: my NO₂ is currently around 1 ppm, and NO₃ is about 40 ppm. That’s a huge increase for a new tank, and the parameters keep changing rapidly.
Regarding nutrients, I’m familiar with Liebig's Law of the Minimum. To avoid trace element deficiencies, I’ve been adding a trace element fertilizer (
Flourish), which I also use in my freshwater tanks. I noticed it’s quite similar to fertilizer such as ChaetoGrō, which are commonly used to grow algae, so I thought it might work here as well? (I’ll also consider getting some liquid kelp, as you suggested)
Since 40 ppm nitrate is quite high, I’m guessing the issue isn’t nutrient-related. It seems my Caulerpa is getting covered by diatoms, which can be blocking light and growth. Is there a way to remedy this?