Hornwort plant help

I have a 15W fluorescent bulb, and I'm using Leaf Zone plant food(liquid). I don't have anything that I can use to measure the nitrate level. Hope this helps.
I have the same amount of light over my 10g and my hornwort is out of control. I got some Ludwiga, crypts, ocelot and hair grass. The grass is the only thing not going nuts. Could it maybe be your plant food?
 
Is your hornwort stuck in the gravel or wedged behind something or is it allowed to float around on its own? Any attempt to force it to grow in one spot can lead to browning and loss of needles.
 
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