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I'm struggling with my 20-gallon long tank, which has been running for seven months. I've got a heavily planted setup with Eco Complete substrate and a 48W full-spectrum LED light on a 16/8 day/night cycle with a night light. Seachem fertilizer and Fritz Aquatics trace elements are being used, along with weekly 40% water changes. I've also got a piece of Mopani wood in the tank, which adds a hint of tea-color to the water.

Everything was going great, especially with the floating hornwort – I always had more new growth than I knew what to do with. But over the past couple of weeks, things have taken a turn for the worse. The hornwort's now struggling to grow, with short starts of new, branching growth that halts and turns brown before recovering briefly. It's a downward trend.

On the other hand, my Red Water Lily is thriving with over a dozen pads and making more. Valisneria's sending out runners and getting really tall, while the Water onion looks okay and is splitting off pups. The "Marimo moss" balls seem to be doing fine, Java fern's okay but not great, and Java moss is just holding on. Aponogeton's not doing well, dying back like the hornwort.

I've tried increasing the fertilizer and trace dose by adding it every other day, but I'm not sure if that's helping or making things worse. I've also reduced the light intensity to 60% since I read that moderate light is generally better – my 48W LED might be overkill for a 20-gallon tank.

Any ideas would be appreciated.

Some more tank specifics: my pH is generally around 7.4-7.6, which seems a bit high but apparently that's okay these days. The tank's well filtered and aerated with an oceanic_42 HOB, 2 sponge filters, and 2 air-pumps. Nitrogen cycle readings are negligible, and the make-up water's hard, so the KH and GH are within acceptable bounds for the fish.

Temp's at 74F, maintained by a heater. I've also got a mix of fish and inverts in the tank, including Corys, Yoyo Loaches, a pleco, a Chinese Algae Eater, a Black Ghost Knife, ghost shrimp, nerite snails, a Rabbit snail, and hundreds of burrowing snails.

I'm going to take a bit of a wild guess here, but could it be a nitrogen deficiency at play? I know it sounds counterintuitive, especially given the tank's overall health, but I've read that hornwort are notorious nitrogen hogs.

farmhand wrote: ↑Tue Feb 11, 2025 6:23 am I'm going to take a bit of a wild guess here, but could it be a nitrogen deficiency at play? I know it sounds counterintuitive, especially given the tank's overall health, but I've read that hornwort are notorious nitrogen hogs.

Thanks for the suggestion, it's definitely an interesting angle. I must admit, I haven't really considered nitrogen deficiency as a possible cause, despite using Seachem fertilizer and Fritz Aquatics trace elements.

You're right that hornwort is a heavy nitrogen user, so it's possible that it's just not getting enough. I haven't specifically addressed a nitrogen deficiency, but I have been increasing the fertilizer and trace dose by adding every other day, hoping that would help.

What would you recommend I do to remedy a nitrogen deficiency? Should I add a nitrogen-specific supplement, or just continue to increase the fertilizer and trace dose?

I'd suggest easing up on the cleaning and filtering. Let the nitrates build up a bit, around 10ppm but under 20ppm, see if that makes a difference. These plants get their nutrients from the water column, not the substrate.

I had a similar experience with floating hornwort - it did great for months, providing a safe haven for my tetra fry, but then it suddenly started browning and shedding leaves. I managed to salvage a few healthy parts and transferred them to a tank near a bay window, which gets more direct light. Unfortunately, even with the better lighting, the hornwort didn't recover, and I eventually replaced it with salvinia and frogbit. The frogbit has been a hit with my tetra fry - they love hiding in it, as you can see in the second photo, where two of them are waiting for food.

"I'm thinking maybe it's not just one thing, but a combination of factors that's causing my hornwort to struggle. I've been reading that sudden changes in temperature and water chemistry - we're talking pH, GH, and KH here - can be a real killer for these plants. Now, I know my tank's been pretty stable, but I've also been tweaking things lately, like increasing the fertilizer and reducing the light intensity. Maybe I've inadvertently created a perfect storm that's stressing out my poor hornwort. Anyone else have experience with this kind of thing?"

farmhand wrote: ↑Tue Feb 11, 2025 6:23 am I'm going to take a bit of a wild guess here, but could it be a nitrogen deficiency at play? I know it sounds counterintuitive, especially given the tank's overall health, but I've read that hornwort are notorious nitrogen hogs.

I had a similar experience with my floating hornwort. It turned brown and lost leaves after several months. I think it was just worn out, to be honest. I had been using it as a hiding place for my tetra fry and it worked great for a while. Eventually, I moved the remaining bits to a tank that gets more natural light, by a bay window. Now I've replaced it with salvinia and frogbit, which the tetra fry seem to love just as much.

farmhand wrote: ↑Tue Feb 11, 2025 6:23 am I'm going to take a bit of a wild guess here, but could it be a nitrogen deficiency at play? I know it sounds counterintuitive, especially given the tank's overall health, but I've read that hornwort are notorious nitrogen hogs.

I was considering a similar approach, but I appreciate the specific guidelines you provided. I'll give it a shot and see if letting the nitrates reach 10-20ppm makes a difference.

I've had success with hornwort in a smaller tank, a 3-gallon setup, where it's been thriving without any issues.

farmhand wrote: ↑Tue Feb 11, 2025 6:23 am I'm going to take a bit of a wild guess here, but could it be a nitrogen deficiency at play? I know it sounds counterintuitive, especially given the tank's overall health, but I've read that hornwort are notorious nitrogen hogs.

Sometimes a water change will help if the water has the missing nutrient your plants need - that can help, but the mineral content of tap water can change seasonally, so sometimes it works and other times it doesn't.

How much water do you replace in your aquarium weekly? If it's less than 50%, it might be helpful to increase the amount. I'm not saying you're doing it wrong, but just something to consider.

Also, you never want to see zero ammonia, nitrite, and nitrate - if you do, you have a nitrogen deficiency. I would recommend a minimum of 5ppm nitrate, that would satisfy the plants' need for nitrogen. You can use Seachem nitrogen to do that quickly.

farmhand said:



My nitrogen cycle readings are negligible, and the make-up water is definitely hard, so the KH & Gh remain within the bounds acceptable to the fish.


What are the actual numbers? What you believe is acceptable might actually be a problem. While we would like to think that fertilizers have everything plants need to grow, the fact is that most are not complete and many are not well-balanced. Seachem has very little nitrogen, calcium, magnesium, zinc, and copper. I couldn't find any information on Fritz Aquatics trace elements, so I'm not sure about that one. If increasing the dose doesn't work, you can try Seachem trace to see if that helps. For my tank, I eventually stopped using manufactured fertilizers and made my own trace, GH booster, and dosed nitrate to 10ppm and phosphate to 1ppm.