Duplication is very tough in hobbyists' tank to compare the rates.
You also need to take into accounts any denitrification/DBS variables.
Over all and this is justa relative figure, the Chaeto is about 1/4 faster.
Chaeto has more surface area and is able to tolerant a wider range of NO3 levels than Cauplera. Caulerpa does not tolerant low NO3 levels well and they starvation signalling upregulates spore production and it goes sexual, much like plants do when spring rains come and they pop up flowers.
If you add a little more KNO3, the Caulpera will be fine.
Adding KNO3 will also drive PO4 levels down FYI.
Limiting PO4 has few negative effects on weeds.
But overall, the Chaeto is a superior choice for it's wider effective range more so than the uptake rates, biomass needs to be standardized if you make comparisons, and actually patch clamping the cell membranes from the protoplast and measuring the flux in the concentrations across is one of the best ways to measure the relative uptake rates of various ions.
The other method is using N15 or the nutrient isoltope of choice and tracing how much is utilize by the plant with enriched N15 etc.
Requires a mass spect and some other not so cheap equipments and a lab tech that does not mind you using their mass spect with enriched higher levels of N15 which makes the natural measurement back ground level testing a pain if you go back and forth. I think they hate me :bum:
Regards,
Tom Barr