[Seadon]

I have root zone tabs from aquarium fertilizer.com and it says they last 3-4 months but it doesn't say how much coverage they provide. My substrate is an aquarium sand and gravel 65/35 mix


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[Diana]

In looser substrate there is more water flow so the nutrients will spread out some, but also diffuse into the water column where the plants can take them in via the leaves.
In the case of a blend of sand and gravel the gravel does not count. The sand has filled all the spaces between the gravel and it is like not having any gravel at all.

So now we are down to 'what size sand particles?'
Something like pool filter sand, blasting sand and other graded materials will still have a reasonable amount of water movement.
Play sand or other sands that are practically dust have much less water movement.

The other thing is that the larger plants can send their roots quite wide spread in the tank, so no matter where the tablet is, the well established plants are probably benefiting.

 

[Seadon]

Wow, thank you, that gives me a good idea of the concept, I have to extrapolate that given a large enough volume of larger sized particles must have some sort of effect on water movement through the substrate, although I am agreed that at the ratio given my tank it is just about negligible, however in the root zones the mix of gravel is much more rich probably as much as 30/70 sand to gravel.


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