Sand Cap On Lava Rock Substrate?

I have a 50 gallon - 36"x18"x18", Heavily planted, with a 2.5" lava rock substrate.

Can I put a 1" to 1.5" sand substrate cap on top?

This is mainly for cosmetics, but would also allow me to buy a school of Sterbia Corys

My concerns:

1.) Will the sand fall through the lave rock over time and end up on the bottom?

2.) The lava rock substrate is doing a great job enhancing my water quality, I believe it soaks up and stores excess nutrients. My Nitrates normally test at 0. Will the sand cap reduce the lava rocks effectiveness?

I'll probably go for Pool Filter Sand, is there a grade / grain size I should look out for?

 

I’m guessing you’re talking about eco complete? In my experience, the sand always ends up going under or mixing with the substrate. It doesn’t do anything special, just like regular gravel, so it’s not storing any nutrients to begin with. (Doesn’t have a high CEC).

Sorry, not sure on the pool filter sand size.

 

I’m guessing you’re talking about eco complete? In my experience, the sand always ends up going under or mixing with the substrate. It doesn’t do anything special, just like regular gravel, so it’s not storing any nutrients to begin with. (Doesn’t have a high CEC).

Sorry, not sure on the pool filter sand size.

It's actually Indonesian lava rock substrate sourced locally here in Malaysia, but yes I was worried that the smaller sand particles would fall through it.

Guess I won't be doing that then.

 

I have sand with eco complete gravel and yes it does mix the sand ends up at the bottom. Still a cool look depending on how much rock to sand you have, mine is more sand than gravel.

 

Couldn't find anything specific to my Indonesian Lava Rock regarding it's CEC, but I did find this:

"Depending on its source, most lava contains some heavy metals and potentially some minerals useful to plants. The CEC of lava is highly variable, but generally hovers between 15 and 40 meq/100g."

Source:

https://www.colinlewisbonsai.com/Reading/soils2.html

So considerably more beneficial to plants than sand or plain gravel from what I can tell.

 

Hello, if capping won't work you might try making area in or one side of tank w/ some type aquarium safe diy barrier or gaurd to keep the 2 substrates from mixing. This will give corys a place to to hang. Hope this helps!

 

Couldn't find anything specific to my Indonesian Lava Rock regarding it's CEC, but I did find this:

"Depending on its source, most lava contains some heavy metals and potentially some minerals useful to plants. The CEC of lava is highly variable, but generally hovers between 15 and 40 meq/100g."

Source:

https://www.colinlewisbonsai.com/Reading/soils2.html

So considerably more beneficial to plants than sand or plain gravel from what I can tell.

It doesn’t say what minerals are available? One i’ve heard people say eco complete(which is lava rock) has iron available. I was always curious where they got that from as it doesn’t say that anywhere. But it’s false. Another substrate that gets compared to eco complete is Seachem Flourite. It’s just regular hardened clay. These 2 are always recommended as a substitute for each other, or to use as a ‘planted tank’ substrate. It has the CEC of 1.7, so that comes to show that lava rocks(or eco complete) is either equal or close to that number. While sand and gravel have 0 CEC..

https://sfwcf.com/pam/pam2c.pdf

 

"Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt."

Source:
Basalt - Wikipedia

Rich in calcium, magnesium, and potassium.

Source:

 

"Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt."

Source:
Basalt - Wikipedia

Rich in calcium, magnesium, and potassium.

Source:

It might be different since they’re constantly submerged. Even then, a CEC of 14(after maturing) isn’t alot.
I use Eco complete(lava rocks) in my tank and my plants still deal with iron deficiency.

 

It might be different since they’re constantly submerged. Even then, a CEC of 14(after maturing) isn’t alot.
I use Eco complete(lava rocks) in my tank and my plants still deal with iron deficiency.

The study shows that mixing lava rock in with a very low CEC soil increased the soils CEC to 14, presumably the lava rock has a much higher CEC, as stated above typically between 15-40.

I'm using 100% lava rock, not trying to enhance a soil, my substrate is also constantly submerged.

I can't talk for Eco-Complete as I've never used it.