I have some rotala macrandra and mexicana in my 180Gal tank.
Whilst they grow very well, I don't seem to have a way to bring out the deep red colour in them.
I dose very close to EI and my CO2 is at 30ppm.
The lighting is 3 x 150W Metal Halide and the rotalas are close to straight underneath the globes.
How do I best bring out the colour in these plants? In particular, the rotala mexicana is only dull pink

Try less light, softer KH, but higher GH.


Regards,
Tom Barr

Thanks Tom,

I'm rearranging the tank this weekend and will therefore be draining around 80% of the water out which gives me a good opportunity to readjust the water parameters.
What about fe?
Does higher fe stimulate the red colour?

Folks often say that, there is not evidence I am aware of that that is the least bit true with respect to aquatic plants but I see no reason other than general limitation, non specific to red color intensity.

Adding Fe might simple remove a limitation, say by increased NO3 uptake, causing the plants to turn redder as NO3 become more limiting.

Not one person has ever ruled that one out to date. You have to be able to isolate and address that issue in particular otherwise it's mere speculation that Fe does anything.

The pathway that is involved in the production of red pigment really does not have much Fe in the enzynmes and there is no iron in any red aquatic plant pigment, it's all C, O, H's, N is present in Chl a and B and mask the red color when the leaves are not stressed and matured(that's why new leaves and fast grow rates produce reddisg tips, not because they are closest to the lights).

Young leaves have very little Chl in them but have anthrocyanin which is what imparts red color.

It's a sign of immature leaves and stressed mature leaves.

Regards,
Tom Barr

I'm glad you mentioned the iron as I've never noticed it makes any difference to the reds. The only way I've managed to increase the reds is to limit NO3 but only able to do for short periods.

I'm curious you mentioned lowering KH. I'm running about KH4 and GH8 at the mo, so do you think that lowering KH any more might increase the reds? Currently running at 2.8wpg of T8.

James