How To Measure Carbon for Precise dosing?

[VR28man]

So, I'm thinking of doing a planted marine tank (seagrass and macro algae), and some of the folks have alleged that I should maintain a 150:30:1 ratio of carbon:nitratehosphate.

Presumably carbon should be measured in PPM? (I'm not so clear on this). I would maintain carbon by vinegar or vodka dosing. Given that, are there any formulae available that would let me gauge how much vinegar/vodka I should add to 1G seawater to move up measurable carbon by x ppm?

Or is this just a matter of "if your pH is in a stable range and your alk is stable, just dose the amount of carbon you need to keep the pH in a stable range".

Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

I don’t think the hypothetical basis makes any sense. Marine plants do not need any particular ratio of N and P. They just need enough of both, as well as many other elements including iron and manganese.

They also do not have any need for organic carbon such as acetate in vinegar, and may not use it at all.

even if these things were not true, before you decided organic carbon dosing was needed to attain a particular organic C value, you’d need to know what the C level was before dosing.

I can certainly tell you the amount of carbon in a teaspoon of vinegar (0.1 g) or vodka (1 g) I just do not see how one would usefully use that knowledge.

 

[Randy Holmes-Farley Verified Community Expert]

As to the pH, I'm not sure how that question relates to the CNP ratios, but some marine macroalgae and plants (but not all) can benefit from lower pH since it can help them get CO2 more readily.

I discuss that here:

Photosynthesis and the Reef Aquarium, Part I: Carbon Sources by Randy Holmes-Farley - Reefkeeping.com

http://reefkeeping.com/issues/2006-10/rhf/index.php

 

[VR28man]

Thanks, Randy. Yeah, I'm curious about the empirical basis for that supposed ratio, to say nothing about how I'm supposed to keep carbon at 5x nitrate. But either way your posts are useful.