Hornwort is benificial as a user of nitrate, absorbing much more nitrate than many other aquatic plant species.
The Benefits Of Hornwort For Reducing High Nitrate ...ShunCyhttps://shuncy.com › Houseplants › Hornwort

 

Hmmmmm......
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For the local/CF input on that plant species, go to post #2 in that thread.

 

So has to be planted with at least 3 inches of substrate (mineral based).
What if don't have high nitrates?

 

If the plant has access to nutrition with it's roots (Nutrient rich potting soil), then a source of High Nitrates in the water will be unnecessary. The plant will grow strongly with the trace nitrates/phosphates it is able to scavenge out of the water of your aquarium system.
Without providing those roots access to a source of nutrition for them though?
Look Out!
The Hornwort could collapse, causing all sorts of problems for you in the aquarium.

 

Noted... Thanks fellas

 

So has to be planted with at least 3 inches of substrate (mineral based).

Nope. My own planted aquarium has 1” max and not over the full area. Plant substrate under the sand/gravel might help in a brand new set up for a short space of time, but honestly, most plants will draw nutrients from the water.

I have fine gravel and the plants do fine. If you want to boost you can use root sticks or a liquid fertiliser andif needed supplement with liquid CO. Pick easy plants and the biggest issue will be keeping them from taking over the tank!

 

Gotcha! Thanks guys