My plants are showing signs of iron deficiency and possibly calcium.
This is more than luikely, CO2 related.
I've never seen a Ca++ deficient aquatic plant in 20+ years.
The only way one might do that is having plain sand, inert.....and RO water.....and not dose Ca++ at all... for sometime.
It's possible, but exceedingly rare.
If you ever feel something is deficient, add more, a very simple solution to rule out such possibilities. Wait 1-3 weeks etc. If nothing improves, then you know it's something else.