Black growth on plants...what is it?

Hi guys

this photo is from a small (64L) tank that has sand as a substrate. The lights (LED) are on for about 10 hours a day and I feed most days with 5ml of Flourish Excel. No plant tabs.

The black covering is on most of the leaves of the broad leaved plants. There is also some green algae clinging to the stems of the thin leaved plants.

PH is 8.5. Is that the problem? If so, how to fix?

Are the lights on for too long?

Any assistance would be appreciated.

That be the dreaded blackbeard algae. Pinch off the affected leaves and shorten the amount of time your lights are on to 8 hours, see if that helps. In fact, if you can lower the light intensity that would be better, if you can't adjust it you could cover some of the LEDs with some black tape if you have any.

Someone else with fertiliser knowledge may be able to help you with your dosage

CaptainBarnicles said:

That be the dreaded blackbeard algae. Pinch off the affected leaves and shorten the amount of time your lights are on to 8 hours, see if that helps. In fact, if you can lower the light intensity that would be better, if you can't adjust it you could cover some of the LEDs with some black tape if you have any.

Someone else with fertiliser knowledge may be able to help you with your dosage

Click to expand...

Thanks. I thought it might be that. I'll turn the lights down and keep them on for just a few hours a day.

Flourish Excel is not a fertiliser, it's a "liquid CO2" Many of us won't use it as it's glutaraldehyde, a powerful disinfectant. A fertiliser which contains plant micronutrients would be better, such as Seachem Flourish Comprehensive Supplement for the Planted Tank or TNC Lite.

Alage grows when lighting and fertiliser are out of balance; too much or too little of one of them. Your lights are on for a long time, but if all you add is Flourish Excel you aren't adding any fertiliser, so there's a clear imbalance there.


As for the dosage of Flourish Excel, that's 5 ml per 40 litres the first time, then 5 ml per 200 litres, so adding 5 ml every day is way too much.

Essjay said:

Flourish Excel is not a fertiliser, it's a "liquid CO2" Many of us won't use it as it's glutaraldehyde, a powerful disinfectant. A fertiliser which contains plant micronutrients would be better, such as Seachem Flourish Comprehensive Supplement for the Planted Tank or TNC Lite.

Alage grows when lighting and fertiliser are out of balance; too much or too little of one of them. Your lights are on for a long time, but if all you add is Flourish Excel you aren't adding any fertiliser, so there's a clear imbalance there.


As for the dosage of Flourish Excel, that's 5 ml per 40 litres the first time, then 5 ml per 200 litres, so adding 5 ml every day is way too much.

Click to expand...

Thanks Essjay I'll swap to one of the fertilisers you suggest and stop using Excel.

Agree with @Essjay and will just add that you need to establish or re-establish the light/nutrient balance or this algae will have an advantage and spread. The duration and fertilizers is the easiest to adjust (rather than getting different lighting for example). Floating plants also help by providing some shade. Do not cut off leaves with algae unless they are dead, this can cause more harm. These plants have mobile nutrients that they can move from old growth to new growth, and until the leaf stem is clearly dead at the bottom (where it emerges from the crown) the nutrients may be moving for the plant's benefit.

The spectrum is also crucial here, do you know the Kelvin rating?

And you're in the UK so my choice would be TNC Lite. Flourish Tabs for the swords would really help, these are heavy root feeders and the nice thing about the nutrients in Flourish Tabs is they do not get into the upper water column.

Hello. Black beard algae can be very natural looking if kept under control and some removed periodically. It's like trimming your aquatic plants. As it grows, it forms a carpet over a leaf. When the carpet begins to cover the leaf, it can be easily pealed off. I just toss the pieces in my composter. I like to leave some of it because it gets a little thick and I like the look of it. But that's just me. If you don't like it, peal it off the plant leaves every time you change the water. You might consider reducing the amount you feed. This will slow the growth of the algae.

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