Thankfully the cycle phase is over already, but I plan on still checking once or twice a week. Copper might be good as the complex has copper plumbing, but it hasn't been a problem so far. Hardness might be interesting, but my pH has been perfectly steady so far and it's brackish so it'll get buffered by the marine salt every week anyhow. I'm honestly not likely to do anything about the dH unless it's very, very bad for the fish (pretty confident it won't be). I haven't had any real algae problems so phosphate seems wasteful, and the only thing affected by calcium is a lone nerite snail.
So, ammonia and nitrate perhaps? Assuming they keep.
