Plants rotting.

[Stormisan]

Some of my plants are rotting, and they don't look too good. What can I do to make them healthy again? I use Tropica premium nutrition for fertilizer every week, and my substrate is around 2 inches. I also give them plenty of light. I contacted the seller and they said that the plants I ordered from their shop weren't grown underwater, so it could be a co2 deffiency. Please help!

[Aiken Drum]

What you are probably seeing is normal with new plants and is called melt.

Your seller is correct that plants are cultivated emersed (not fully underwater). Emersed plants have ready access to CO2 from the atmosphere, and can therefore grow quicker and make commercial aquatic plant growing more commercially viable.

What that means for your plant though is that when you put it in your aquarium fully underwater, that CO2 is largely cut off, and the leaf structure cant cope with the change and melts. This isnt to say you need to be injecting CO2 though. New growth will be more tolerant to its environment, and get CO2 from the water through a different mechanism to what the original growth did from the atmosphere.

This can all take time though. Judging plant growth over a few weeks isnt giving them long enough to transition from emersed to submerged. Are you seeing any new growth?

The thing to do is remove any leafs that are dead or dying so the plant isnt wasting resources trying to maintain old growth and can focus it on new healthy growth. You may over time lose all the original growth but as long as its replaced with new growth thats not an issue.

You also should keep low demand plants unless you really want to be getting into specialist lighting and injected CO2.

Ive used the tropica fertiliser before with good results. Rooted plants could also benefit from root tabs in the substrate.

[Stormisan]

Ah thank you. I've had to trim a lot of my plants off as a lot of them have turned brown and yellow. I literally had to pull out most of my ludwigia Repens because they were turning translucent. Some of my frogbit roots have been growing longer, and my Vallisneria spiralis have been growing some new leaves, but other than that, no sign of any other growth.

[Caliban07]

Tropica premium nutrition lacks two of the most important nutrients. Nitrogen and phosphorus. They omit them on purpose because hobbyists over the last 40 years have managed to convince themselves that both these nutrients are responsible for algae growth. This is not the case.

You need an all in one fertiliser like Thrive or TNC complete. Or you can buy dry fertiliser salts such as potassium nitrate and potassium phosphate and use the Tropica stuff for everything else.

Plants take co2 in through their leaves. The mechanism is different because underwater leaves don’t have stomata. The co2 needs to diffuse across the leaf boundary layer. That’s why underwater leaves are thinner, often appear translucent and less waxy. The leaves that are on the plant when you first plant them are not completely useless though. They have carbon storage and the plant will use that storage to grow new leaves under water. But it’s a slow process.

Once the carbon stores are depleted, the plants then have to rely on these new leaves to take in co2 to create energy to grow more leaves so it’s an exponential pattern. The more new leaves there are, the more co2 can be captured and the faster the plant will grow. This is why patience is imperative.

Some things that will help with the process are:

1) Providing all necessary nutrients
2) Increasing carbonates hardness
3) Reducing light intensity

Light drives photosynthesis which requires co2 and the more light the more co2 is needed.

Plants can also use carbonates as co2 so increasing KH if you have soft water is a good idea.