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Floating Plants Failing to Thrive

7634 Views 8 Replies 6 Participants Last post by  Funkycamel
I like to use floating plants as a fertilization indicator in my low-tech tanks, because I know that CO2 is never a limiting factor for them. I recently started a 20L tank, planted with various crypts, some bacopa monnieri, compact amazon swords, and some hygrophila spp. For floaters, I put in red root floaters and amazon frogbit. The substrate is about 2 inches of ecocomplete over a thin layer 1/4 inch of peat moss and a sparing amount of osmocote plus.

After a couple of weeks, I can't seem to get the frogbit and the red root floaters to thrive---the roots seem to die, and the leaves turn yellow and start to melt. This goes for healthy frogbit that I move from my other established tank. Likewise, when I move red root floaters to the other tank, they also do well. There is some current in the tank, but I have corralled them so they don't move, and the current is no greater than in my other tank, where the frogbit is doing well.

It almost seemed to get worse when I added small quantities of fertilizers (KNO3, Seachem Equilibrium). I've seen the effects of low potassium on frogbit (waffle pattern browning) and this seems very different. The underwater plants aren't as badly affected, but they so are establishing themselves as well as I think they should, and the bacopa seems to show inter-vein chlorosis on new leaves. I think the same thing that is happening to the floaters is happening to the other plants, but more slowly.

The ammonia was about 0.5 ppm, the nitrite was about 0.25 ppm and the nitrate was about 5 ppm last time I checked on Saturday.

Pictures are attached.

Has anybody seen something like this?


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I like to use floating plants as a fertilization indicator in my low-tech tanks, because I know that CO2 is never a limiting factor for them.
That's clever.

Just a shot in the dark: is there a difference in temperature between this tank and the others? I know water temperature isn't something we talk about a lot on here, but I have noticed that floating plants can be a little sensitive.
I may have had the temperature a bit low (like low 70s) for the first bit, but I've tweaked it up slightly, so the temperature is now between 73.5 and 75. It's possible that might be a factor but I doubt it. I've kept frogbit in unheated bowls (in the 60s) and it has done just fine.

I had thought earlier that there might have been an issue with the peat and/or osmocote leaking into the water column, but the ammonia/nitrates are not that high for a new setup, and the pH (7.4 or so) is not as low as it would be if the peat was leaching into the water column.
Ack! I have that exact same problem in my 12g betta tank - frogbit just refuses to grow, roots fall off and leaves melt and turn yellow. I also have frogbit in a small unheated and unlit bowl and it thrives there. So annoying!
I cant seem to get frogbit dwl or rrf to grow in my low light shrimp tank either. I figured it was lack of ferts.
Moss, subwusserstang and blyx grows fine though.

I just through it away each week and replace, so it doesnt look shabby
I'm thinking of trying to add additional fertilizers, because I can't really imagine toxicity is an issue at the levels I'm seeing in those nutrients I can measure. Besides, with no inhabitants in the tank. Could the fresh substrate with high CEC be taking nutrients (Fe perhaps?) out of the water?
My issue was the opposite. I had RRF, and accidentally some duckweed. The stuff grew so well that I had to remove it all.... Within 2 weeks time, it would multiply to cover the whole surface of my 75, causing light issues with the plants underneath. All I can say is that they like ALOT of light. I have 2 Ecoxotic 120 over mine, 6" away..... So close I thought that they would burn. No. They multiplied.... Alot.

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I have some more observations to share: Underwater plants are definitely showing inter-vein chlorosis--it is visible in the amazon sword, the moneywort, and some of the crypts as well. The frogbit loses its roots, but in addition, the plant nodes themselves are browning. This is probably a result of the struggling plants rather than a cause, but I do notice a thin oily sheen on the surface.

I am pretty sure this is not a potassium deficiency--that creates a waffle-pattern browning in frogbit. I've had that before, and upping the dose of equilibrium and/or K2SO4 eliminated that problem effectively in the past. The browning here is more large patches rather than a waffle pattern.

Ther inter-vein chlorosis suggests to me either magnesium or iron deficiencies--I have added both in the last couple of days: Flourish to 0.2 ppm iron, and about 1 tsp of equilibrium (for Mg), plus enough KNO3 to raise the Nitrogen by about 5 ppm.

The only other option in my mind is a phosphate deficiency. If I don't see improvement in a couple of days, I'll add some potassium phosphate.

This is so puzzling, given that both the RRF and the frogbit do well in my established tank. The recovery/deterioration when I move plants back and forth is remarkably fast.
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Potassium nitrate will drive up your pH. Not sure about potassium phosphate. Browning on old growth indicates potassium deficiency or potassium unavailability. Interveinal chlorosis is iron deff in new growth and magnesium in old. Epsom salt can help and it is good for the fish. See Mulder's chart for plants
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