90x45x45 ADA setup

1. I do not know if you have continued your 50% water changes. If you stopped after two weeks you need to begin those again. I am not a user of aquasoil, but I believe at the beginning aquasoil leeches a lot of nutrients into the water column, so you must keep up with water changes at the beginning.

2. If you are running 4 T5's you need to increase your CO2 saturation and increase your lighting period. With the amount of nutrients you have in your tank with the aquasoil and E.I ferts, you do not have significant plant mass to use the majority of those nutrients in a 5 hr period with that intense of lighting. So you have a lot of excess nutrients left over in the water column since you are only running your lights for 5 hrs.

3.So in my opinion you need to do several things. I would start by increasing my CO2 along with adding a couple hrs to your photo period and possibly turn off one aquaflora bulb. Continue with weekly or multiple weekly water changes.

Unfortunately you will have to experiment with somethings before you see results. There is not magic solution here. No one here can give you a definite solution to your problem. There is some trial and error. Start with what I suggested and tune your system from there.

I just realized you only have a HOB filter on your tank. You might want to add a powerhead or circulation pump to move the water around a bit more in your tank. It could help with algae prevention in the future.

If you still have diatoms, you have to continue with your water changes. On a slightly different note, an entire scape of mine was once ruined by diatoms. I would do 50% WC's daily and it only seemed to feed the diatoms. My well water passes through a sandy layer. I figured that out of course once the tank was beyond recovery. My water changes were literally feeding the diatoms their silicates. Normal tank progression is that diatoms show up and kill themselves by consuming all the silicates, their lifeblood. Now I use exclusively RO/DI and dose to desired hardness (my seiryu stones do most of that for me). Solved the problem, no more silicates, diatoms never even show up in new scapes. I'm in the process of a new cycle right now and I'm positive I won't see even one thread of that diatomaceous gunk. I really feel that if you're willing to do it, using PURE RO/DI water is the best way to go; it gives you a blank slate to get your water exactly where you want it to be, you just have to know what to dose.

Forensicfish gave you some good advice, use it. Also, you will need to increase your CO2 even more so due to the surface water disturbances caused by your HOB filter.

Hope that helped somewhat, Forensicfish got most of it.

ALSO, don't underestimate aquasoil, most people don't dose a thing for the first month or so on fresh AS.