Agronite is a good choice for a substrate, its what I use mixed with sugar fine sand. With that said it doesn't matter what kind of sand you use you will see algae as your tank cycles and balances its self out. When I started mine up I got the lovely diatoms and then cyano
popped up shortly after. When I got everything in balance no more algae. I don't care what kind of rock, substrate fish no fish coral no coral whatever if you have a balanced system you wont have the algae problems. What that means is correct PH, SG
0 ammonia 0 NitrItes 0 Phosphates 10 or less NitrAtes frequent PWCs good salt mix, RO
water and proper feeding along with a good amount of LR
and a good working skimmer. Take a leave out of natures book and try to imitate that in your tank and you will do well.
My sand bed in my tank goes from 2" to as deep as 6" in areas. Sand is one of those things that people don't always agree on. It's more of a personal choice.