Why would you use Phosphate remover? Are your phosphates elevated? Are you assuming they are elevated because you have cyano?
First thing to do would be test phosphates. As for the Redfield ratio, are you trying to reduce phosphates or remove the cyano? I wouldn't necessarily interrelate the two. If your goal is to remove phosphates, GFO or analogous compounds will do the trick most simply and are a commonly applied solution. If your goal is to remove cyano, save yourself a huge hassle and start out trying ChemiClean. IMO, dosing nitrogen would be way down on my list of things to try.
On a side note, just because your nitrates are at, or close to zero, doesn't mean nitrates are not around and available for organisms to utilize, it just means they are being taken up as fast as they are being released. Right now your cyano might be using up the Nitrates more efficiently then other stuff in your tank. Were this the case, adding more nitrogen could bloom the cyano even more. I'm not saying this is the case, just one possibility. Start with chemiclean and if that doesn't work let us know and we can move to plan 'B'
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Dan