Planted shrimp tank substrate

[Coastiefisho]

I’m going to start a seperate planted cherry shrimp nano tank (55 litre) and was trying to decide between two different substrates seachem flourite black and caribsea eco complete. Was wondering if those who have used either of these could give me their opinions or experience of it. I’d prefer either of these two as my PH is naturally on the lower side somewhere between 6.5 & 7 so I don’t want anything that will lower it further thanks.