Black spots on the plant leaves - please help

HI all

I had an outbrake of black beard algae in my 16g tank. did some research and started to use flourish excel, which seemed to do the trick but now I have those black spots spreading across all of the plants. please check the pictures and let me know what can be done?

My water previously was high on Phosphapes, but I bought a phosphate removal, which did the trick. here are my water properites:

Amonia 0
Nitrite 0
PH 7.6
PO4 0.03

Thanks in advance!

How much light does this tank get?
  • Thread Starter
I got Twin-Lite 20W PL5 which is 6500 K plus I added sticky foil tape to the hood which reflects a lot of light as well. light stays on for 11 hours a day
Are you sure it's not remains of the BBA? Try wiping it with your fingers.
If not, I've got tips of spot treating these with hydrogen peroxide.
For a planted tank you want phosphates maintained from 0.5-2ppm. You don't want it depleted. phosphates don't actually cause algae.

BBA is usually from low or Co2 fluctuations. Basically an imbalance.

Usually this can be out competed by healthy plants, nutrients dosing and CO2. If you've got plenty of light then you need to balance light, nutrients and co2. Are you still dosing Excel at all?

Reducing photo period to 6-8 hours.

I'd start removing the most infected leaves and continue with Excel dosing.

Your plants look nutrient deprived as they look yellow and little browning. Are they growing at all?

Slow growing plants too are prone to this type of algae if it gets a foot hold.

Do you dose a balanced fertlizer and root tabs for any root feeders?

If root cause isn't figured out it will be persistent.
  • Thread Starter
thanks for all the points. it's great to have some expert advice

It doesn't seem to be a BBA as I can't remove it from the leaves. I'm still using Excel, just a normal dosage according to the instructions. I also add liquid fertilizer Sera Florena, once a week or so. The plants grow a lot and there are a lot of new roots growing from all over the plants.

Previously I had a very hight phosphate (>1ppm - I wasn;t aware how high in phosphates my tap water until 3-4 weeks ago), so I introduced a Rowaphos PO4 remover, which perhaps did too good job.. It didn't make any difference to plants as far as I could see.

I will reduce the light and coninue with excel as you suggest. Perhaps I should switch to root fertiliser instead? any other suggestions?

It looks like BBA to me. This type of pesky algae you can't manually remove off the leaves.

You can also do a weak water/bleach dip for 30 seconds on the hardy infected, and then immediately put into fresh heaviley dechlorinated water and make sure there is no smell of bleach when you return to tank.

You still want to continue with your fertilizer dosing. Root tabs are used in conjunction with water column fertlizers. I wasn't sure if you had any root feeders like Swords, crypts and Vals.
  • Thread Starter
thanks. it makes sense. it's quite widely spread - I will have to bleach most of the plants now. is it the only way?

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