We've discussed substrates before in the
Sand, inert or soil? Which would you pick and why? You can find many opinions on what people are using and what they think about it. We've also talked about
switching from an inert substrate to an active substrate.
I am not a fan of Fluorite because I think the granules are too large and it's harder for plants to root. I've never used the sand version so can't comment on it.
I personally think substrate choice should consider:
- Providing a suitable medium for the plants to easily root in.
- Providing for some separate between water column and substrate solution but too much. You want some exchange happening to get some oxygen into it. You want a good environment for the substrate ecosystem and microbiome.
- It should be aesthetically pleasing to you and fit with your aquascape.
- It should last a certain amount of time that is agreeable to you.
I personally prefer soil-based substrates because I have found them to provide most of the above. They function as a nutrient storehouse and you can add nutrients manually if you want. However, inert substrates can also do this and, theoretically, would last longer as clay tends to compact after a few years.
My suggestion would be not to combine soils as that will cause problems later on. Pick one and stick with it managing it to hit the above goals.