Do you cover the tank with any clear plastic wrap at all?
I was thinking the same thing. I've never seen HC successfully grown with the DSM using a substrate capped by sand...sand is pretty much glass and highly reflective I would assume. That could definitely be a bad thing. I've never used a sand capped media for DSM, so I don't have any story of personal success or failure, but perhaps someone who has, could chime in on that particular part of it.I would keep it wrapped. I've grown HC emerged successfully and found the best method was to cover it well, with rich substrate (aquasoil) and plenty of light. I just started a DS about two weeks ago and the HC is growing well, lots of growth and tons of new shoots. It might be the roots are not able to get to the MG through the sand cap. What kind of light are you using?
What do you have over the fluorite? It needs something capping it if you use it otherwise your tank will be cloudy every time your hands go in the tank lol, its so so messy so when you decide to fill the tank up I would add some kind of sand over it, It's a great substrate just best used as a bottom layer because of the mess, You can get 50 lbs of black or natural colored sand for $5 if you want of course.Already spent the money on the standard stuff, and really don't feel like dropping another $30 on another bag of sand. The HC is planted in individual stems, but a bit sparse for what I'd like, so we'll see how it goes.
If you want black sand go to tractor supply and find black diomand sand blasting sand it's like $5 for 50 lbs, And yes Lowes and home depot have the tan sand called playsand, if you find a pool supply store then you can checkout pool filter sand as well.I personally would go with the black diomand because it just makes everything look better and colors pop! I'm Acually In the process of replacing all the gravel at our store to black diomand, Also doing a 700 Gallon planted tank soon and I'll probably be using it for that as well lol, It's awesome sand.in the past, i've used it rinsed and never had a problem, but i left the dust in for this tank. I have some white sand filling in the gaps where i don't want plant growth, but I don't like the looks of it that much. i suppose a trip to homedepot is in order to find some tan sand. I don't have a good LFS, and my nearest petco is a tiny, worthless one that doesn't stock anything useful. Getting what I need is a bit harder than I'd like.
Pool filter sand didn't work out in my tank. Been told by others too that it is not good for compresses. Lowe's and Home Depot carry pool filter sand. It isn't as white as it is from a pool supply store but of similar grand.Lowes and home depot have the tan sand called playsand, if you find a pool supply store then you can checkout pool filter sand as well.