I use plain gravel with 2-3 mm diameter.
Had been dosing with Osmocote and fert tabs for the first 2 months
and dosing about 1/4 of what Tom suggested (for fear about critter's health).
Then I upped to half-dosage of EI for about 20 days and stopped
substrate fert because pushing tabs into substrate was too time
consuming and the result of it was unclear. The result of dosing
half-dosage of EI without substrate firt was impressive.
And then after reading Tom's mention about toxic level of nitrate
(
http://www.barrreport.com/fish-planted-tanks/4254-no3-vs-fish.html )
and seeing his high fish load 20G tank (
http://www.barrreport.com/fish-planted-tanks/3899-cant-figure-out-lesson-yet.html ).
I started dosing the full dose of EI with fingers crossed.
Tom's suggestion for a 20G tank:
1/4 teaspoon of KNO3 3-4x a week (every other day)
1/16th-1/32nd teaspoon of KH2PO4 3-4x a week (every other day)
Traces added on off days as the macro nutrients, so 3x a week, 5mls each time.
SeaChem Equilibrium 1/8 teaspoon after water change.
My tank is 80 liter, 3 months old, Eheim 2217, 3 WPG for 10 hrs, DIY CO2.
E. Tenellus, Vallisneria, Vivipara, H. Zosterifolia, Blyxa.
1 Angelfish, 1 Whiptail Pleco, 2 Mollies, 3 Sterbai Cories, 6 Otos,
7+1 Black Neon Tetras, 8 Yamato shrimps.
I translated that to dose in liquid daily:
KNO3 5.42 PPM before light on
KH2PO4 1.31 PPM before light on
K2SO4 1.52 PPM before light on (hate to see it unused)
Traces mix 8 CC after light off (much higher than suggested though
to test Heteranthera Zosterifolia)
Fe-EDDHA around 0.015675 PPM after light off (higher than this
the water turns too red)
Dry dosing at water change:
CaSO4 1/4 tsp
MgSO4 1/4 tsp
Plants are growing fast and looking better overall.
Blyxas grow much bigger in short time even thoug this plant
is often referred to as a heavy root feeder.
Fish/shrimp health seems OK, actually a baby Black Neon Tetra
appeared out of nowhere 3 days ago. They seem to mate every three days.
So water quality should be OK.
The fert tabs may help initially to help plant's establishing (?).
But anyway, if I could restart it, I would lay some sort of substrate fert,
such as the Tropica Plant Substrate to avoid the chore of
pushing tabs in the first months.
I still not satisfied with my tank though, struggling with quite an amount of
Spirogyra (I believe) a tiny bit of BBA, and H. Zosterifolia melting.
It looks OK 3-4 meters away, certainly not at 50 cm distance
(hope it will be some day
). But at least this tank's substrate is all plain gravel,
so to your question, I think it's possible.
BTW, the stuff at Tenellus's base (just mowed—used to be taller than
the Blyxas) close to the the glass in the picture is brown debris that the
Ottos can't access to.
