I use the stainless clamps in my tanks sometimes. The rust is not a huge issue and people put it in their tanks in the form of GFO. Replace it when you can because it will eventually fail, but don't lose too much sleep over it if you don't get it done soon.
Nitrate and phosphate are not linked chemically, but they are biologically. Anything that grows in your tank will need to consume phosphate. Some algae will consume nitrate, but they need the phosphate too - some bacteria are the same way. Micro fauna will consumer the algae, but also need phosphate. The organisms also need carbon to grow, but this also gets introduced into your tank when you feed (this is another topic for another day). Typically, you want them both to be low, or high... but not too high. Too high is deadly to inverts. If you used aragonite sand and live rock, then organisms that develop in the tank over a year, or so, will handle the N and P in equilibrium by using aragonite to bond/swap the phosphate and then using it to grow/multiply. A good export mechanism (skimmer) will keep excess out and although it can limit your microfauna growth during peak times by removing fuel, it will also help keep the levels from getting out of control during a fall back. If you interrupt the process of letting your tank fully mature by using vinegar, vodka, GFO, silica sand, dead/dry rock, then you are on your own for processing and the tank will not be able to do it... sometimes never, and sometimes for 2+ years. Here is the bottom line: just let the tank be for a year and it will all get sorted out if you used the right stuff... if you feed high quality foods, then the N, P and carbon are introduced in balance already and should be about the right mix to feed the organisms in your tank.
FWIW - I think that the Salifert test kits are better than red sea... they change color with just one drop (mostly) and are more accurate.
