Hoppy: Wouldn't an imbalance like 5 ppm nitrate to 20 ppm phosphates cause an issue? I know a high phosphate amount in relation to a balanced nitrate amount doesn't cause problems. In fact I've witnessed better coloration this way. That's why I what the nitrate measurement too.
Anthony, Hoppy is correct, but so are you.
Hoppy is right in that there has been no evidence of PO4 abundance leading to algae....none, It was once thought that it did, but that is not the case.
You are correct in the ratios being important, but the limiting factor is Nitrates....NO3 should be at a higher concentration than the PO4 optimally, but again, depending on the Carbon concentration, the plant only uses so much, so as long as you have enough, that is fine...excess is drained out when you do your water changes.
Same holds true for PO4...if you have excess, it simply will not be used, and will reset when you do your water change. That is the principle behind EI...even though your ratios aren't perfect, have enough of all that the plants need, and reset the parameters during your weekly water change. Testing is good for one reason if you dose EI. If you want to fine tune your regimen as to dose what you need so there is no excess....this is a long process and requires testing and watching your plants to see if there are noticible signs of deficiency over time. Again, EI eliminates the need, and the ferts themselves are not that expensive....your time taken to fine tune all of this is more prescious....so dose em up and take the tankwater from your waterchanges and water your terrestrials with it! They will apreciate it!