Is This Blue Green Algae (Cyanobacteria)?

I've been battling this stuff for a few weeks now. Tank = 6ft planted discus tank. Established 5yrs plus. LED lighting on 8hrs/day. CO2 and liquid ferts. Food = discus granules, flake, dry frozen blackworm and algae wafers - I'm pretty sure the food quantities are not the problem, they don't get fed a lot and the blackworm is fed 1cube/day. 50% water changes every week. Water source = rainwater tank. Moderate level of ambient light as tank is a room divider and located somewhat near sliding door openings. In addition to the main canister filter (Eheim Classic), I have a 'water treatment' filter (Eheim 2213) running Purigen, Phosguard and activated carbon - you can see the results in the phosphate test, virtually none.

I've run a treatment with Excital on the advice of my LFS. In addition I did a fairly invasive cull of affected plants so the tank now looks somewhat empty compare to 'normal'. Following treatment with Excitel, the algae growth returned after a week or so frustratingly I'm back to square one. I'm looking to do an Erythromycin treatment but don't want to run the gauntlet on killing the filter media without knowing what I've got is actually Cyanobacteria.

Is this definitely Cyanobacteria??

Additional photos showing algae problem.

Not entirely sure it's BGA. BGA is green and slimy. Is the stuff on the leaves slimy? Any growing on the substrate? Does it grow on any inert stuff or just the plant leaves? I got some in my tank-see journal.

I am inclined to think the plants are having a bit of a die off after moving to a new tank. Keep them healthy. Manually clean as much of the affected leaves as you can. Are you dosing enough CO2 for the light they are getting? Plant growth is a good indicator.

If its just brown fluffy stuff, it's diatoms.

Are you dosing fertilizer, root tabs for the plants? Why aim for zero phosphates? Plants need some. I dose heaps of dry ferts in my tank.

My aim is lush healthy plants. Algae will grow a bit, but it can't complete with with healthy plants.

Good luck

Thanks Shakti - algae is not particularly slimy. It's not web-like as I've seen with BGA. Only grows on leaves, none on substrate but reasonable amount on glass as depicted in photos. Tank sides I'm cleaning every other day but the ends are difficult to get to because the tank sits between two walls, you can see the red/brown stain on the tank walls at the ends. Plants have been in tank for over a year but have died back recently, I suspect through changes in the water and/or water temp?? I've introduced some new fish (mainly discus) but no new plants. CO2 dosing = 2bubbles/second. Fert dosing = 15ml/week with Seachem Flourish as well as a pond Algaecide, both in liquid form. I have no algae eaters but a relatively large albino pleco who's a recent acquisition but has hasn't made any inroads to the algae problem.

Your comment about the phosphates is a good one - guess I was wanting to keep it low to rule that out but you're right, I need to ensure there's some.

Had thought it may be diatoms but my 'googling' indicates diatoms (or brown algae) doesn't like good lighting - with the LEDs and the amount of ambient light I've had the view that I have too much lighting, so I was ruling that one out.

Thanks for the feedback - hate this stuff, puts such a downer on the tank.

I'd be confident its not Cyano. Whenever I have seen it in tanks and photos of tanks it is definitely green slimy snot and most often on the substrate.

Cheers,
Scott

The more I stare and your pics and read your description, the more I am thinking of wo things:

1. Diatoms-not really true that they don't like light. They have grown in my tank. And it's heavily lit. I have seen it in lakes under the sun. Otolincus will clear it up in no time. Plecos dont really touch it.They do a great job with green dust algae. The one nagging doubt I have is that diatoms are common in new tanks. I don't understand why they would suddenly appear in a tank like yours? Did you a major clean or filter wash that put the tank in a mini cycle?

2. Plant die off-are those crypts.? They are sensitive to water/temp change. Trim off leaves that are beyond help. Clean the rest with a soft toothbrush. Put some root tabs in the substrate. I shove some Osmote for Aquatic Plants tabs (bunnings) and Dynamic lifter.

3. CO2-may not be enough. But be very cautious when dialing up. Discus don't like it. I use up to six bubbles a second in mine, but I have overflows and a sump.