Algae On Floating Plants

[littlest]

My maintenane on my tank hasn't been good recently because I have been ill in bed. I've noticed the last few days that the tank seems dark when the light is on. Today I realised that I have a lot of algae on my floating plants (giant duckweed and frogbit). The algae is a dark but brightish green and is kind of slimy. It's all in amongst the floating plants, so it is connecting all the floating plants together and blocking the light for the rest of the tank.

Tank details:

30L
11W light (~1.4WPG)
Plants: giant duckweed, amazonian frogbit, java fern, java moss, anubias (heavily planted)
Gravel substrate
Normally dose Flourish once a week but missed a dose on Saturday due to illness.
Normally dose Flourish Excel daily but haven't dosed in three weeks because I am treating whitespot with Formalin and the nice people at Seachem told me Excel is not safe to use with Formalin.
Inhabitants: 1 sparkling gourami, 3 amano shrimp
Stats: Ammonia 0, Nitrite 0, Nitrate 30.

The tank is overdue for a waterchange because I have been, and still am, ill and not really up to doing it. Last water change was 9 days ago (50%)

Should I just chuck all the floating plants out? It's seems best to. What else should I do though? Blackout?

Here's some pics:

From above:

From below:

The algae only seems to be on the floating plants so far, although it's a bit difficult to tell as the tank is so dark.

 

[xxBarneyxx]

I get the same thing occasionally in some of my floating plants.

I think it is down to two things:
Not enough CO2 (mine was worse when my CO2 levels dropped low)
Not enough water flow.

I have increased the water flow just under the water surface of my tank to move the floating plants around a little and it seems to have cleared it up (though higher CO2 levels might have done this also). I only ever got this in the floating plants and to be honest I mostly just ignore it.

 

[Liam]

It looks like Blue Green Algae, a three to four day blackout is a good cure for it. A 50% water change is good after the blackout to clear up the dead algae. BGA is covered in Georges alage sticky at the top of the forum.

 

[nry]

If it is only on the floating plants, they grow quick enough that you could rip out any affected leaves/plants and throw them out. No point leaving the algae in the tank on the leaves as this will only help it spread.