Rotala Macandra dark and curling

[LightingBamboozled]

The rotala macandra pictured (behind the fish in many cases) here has been looking well since August when introduced,trimming tops and replanting has been working. However one of the stems has gone dark and curling and all of the stems are looking a little less perky. I'm curious as to if it indicates a lack of something.


1. Tank Dimensions: 152.5x45.5x45.5 (C.250L actual volume)
2. Established: Started Oct 2020, Fish added Nov 2020
3. Tap Water: Ammonia 0, Nitrite 0, Nitrate 0, kH 2-3, gH 7-8, pH 6.5-6.8 degasses to pH 7.4-7.6
4. Filtration and Media: Two Tetra EX1200 plus, half foam, half biohome mixed with ceramics.
5. Lighting and duration: 2x1450mm t5's 80w Giesemann Powerchrome Tropic and 80w Giesemann Powerchrome Super-Flora 10hrs per day.
6. Substrate: Inert small gravel and large sand mix about 1 inch deep.
7. Co2: Reactor on one of the filters, running at around 18ppm CO2. On 5 hours before lights on and off 3.5 hours before lights out.
8. Drop Checker: Yes sometimes. Aiming for Dark Green.
9. Fertilizers: 6ml CSM+B trace elements daily. 1.5ml Flourish Nitrogen Daily, 1/32 tsp Potassium Monphosphate daily. (Occasional sodium bicarb and powdered cuttle shell it's for animals but affects water parameters so worth mentioning)
10. Water change regime: 20-50% per week depending on dead leavs and other mess.
11. Plant list:

1. Vallis Americana since Oct 2020
2. Limnobium Laevigatum since Oct 2020 although new added in August 2022 due to condensation damage on old growth
3. Saggitaria Subbulata since Oct 2020
4. Vesicularia Dubyana since Oct 2020
5. Microsorum Pteropus since July 2021
6. Salvinia Auriculata Since July 2021 (almost entirely outcompeted by Frogbit)
7. Crinum Calamistratum since August 2022
8. Eleocharis acicularis mini since Feb 2023 (almost all outcompeted by Dwarf Sag now)
9. Marsilea hirsuta since Feb 2023
10. Marsilea crenata since Feb 2023
11. Lobelia Cardinalis Mini since Feb 2023
12. Ceratopteris Thalictroides since Feb 2023
13. Limnophila Sessiliflora since Feb 2023
14. Hygrophila corymbosa 'Siamensis 53B' since Feb 2023
15. Rotala Macandra? sincee Aug 2023
16. Rotala Indica since Aug 2023
17. Phyllanthus fluitans since Nov 2023 (recently added to diversify floaters)
18. Salvinia Natans since Nov 2023 (recently added to diversify floaters)

12. Inhabitants.

1. 20 Cherry Barbs
2. 17 Neon Tetra
3. 15 Lemon Tetra
4. 4 Silver Flying Foxes
5. 2 Bristlenose Pleco
6. 25 Amano Shrimp
7. 11 Yellow Cherry Shrimp
8. 5 Nerite Snails
9. 4 Horned Nerite Snails
10. Malaysian Trumpet Snails

13. Full tank shot:


14. Surface and Floaters:

 

[_Maq_]

Well, Rotala macrandra (plus perhaps Rotala indica) is the only one among your plants which belongs into the "sensitive" group. If there's any trouble with nutrients, rotala is likely the first one to display defects.
My rotalas show defects relatively often, and it seems that phosphorus and iron are the usual culprits. Strikingly, you dose both elements daily, which is wrong, I believe. Iron and phosphorus should never be dosed simultaneously.

 

[LightingBamboozled]

Huh! I knew you couldn't mix them into the same fertiliser, didnt realise dosing them around the same time was an issue.

So what would the ideal dosing regimen be. Assuming I water change on a Saturday should I frontload one of them and does the other on the other 6 days or is it best to do them both as single dose?