Hi
1. It is not uncommon for some plants to melt away when planted in new Aquasoil Amazonia.I have had it with foreground plants(Staurogine, HC cuba,Pogostemon helferi....) mainly.I think is sth to do with initial tank imbalance and I resolved it with increasing oxygen levels at lights out by adding air stones on timers when lights are off.
Often those plants bounce back if not melted completely or can be reintroduced successfully after things have settled in 5-6 weeks after the start.
2.That might be just the lamp spectrum some kelvin temperatures make green plants to appear yellow to the eye.
U have Amazonia(very nutrient rich) and U dose so your ferts are covered for deficiencies.
3.Diatoms are not stubborn algae.Once plant mass is increased and plants are established will go away.Meanwhile its easy to rub it off glass and brush it off with toothbrush from stones to keep it in check.
4.Any plants that seem loose can be just pushed down.U dont need to rip all out and replant.
5.Your Tank has quite a large footprint and it seems your flow is only arround 3000l/h wich is quite a low flow for 700+ liters high tech.The rule of thumb is 10x tank volume per hour.
Once plants grow in they will do most of the biological filtration but U need to make sure your flow is good for distribution of CO2 and nutrients as increase in plant mass also will restrict flow.
6.Starting with Amazonia is normally done with large 50% frequently done waterchanges.Everyother day may be enough for first few weeks but U need to change 50% + as minimum and then when U see good growth all arround switch to once weekly.
7.For that size tank and those strong lights I dont know how much CO2 U are dissolving with intank diffuser.It is not one of the most effective metods.
How long before your lights on your CO2 is comming on.U need to achieve the lime green drop checker on lights on and staying that colour for the full lenght of photoperiod.Try to move it arround the tank to see if U have consistency in readings everywhere arround the tank.U can even as advised do a PH profile to get better idea.
Have a look here for CO2 injection and flow in high volume tank.Its a long read but will give U plenty of useful advice.
https://www.ukaps.org/forum/threads/olympus-is-calling-maxspect-gyres-fitted.43046/
8.Algae crew(Amano shrimp,Cherry shrimp , Otos,SAE ,snails
😱)will help with algae but I will wait with that till U get the CO2 tuned up first.
And at least 6 weeks from the start as a minimum due to the Amazonia high Ammonia load.
Any particular reason why U use RO water?
Do U cut it with tap?
Regards Konsa