Hoping I can get some help here.
I've suddenly had my whole tank afflicted by something strange and unidentifiable.
It happened very rapidly and is affecting all the different species of plants in the tank (Anubias, Java Fern, Amazon Sword mostly). It doesn't scrape off like an algae (I assume) would, so I'm wondering if it's a deficiency of some kind.
I took this picture of the leaves on one of the Anubias.
If anyone recognises it on sight, any help would be gratefully received!
Looks like Rhotophyta 2 (sp?) a type of black algae. Lower iron levels and see if your water has free iron from the pipes. Raise CO2 and slowly raise magnesium (MgSO4) level of your water. I call it tar algae. It will not scrape off like you say. Prune affected plants. Bleach dip might help.
Thanks Newt, I will look into your suggestions. I don't have a CO2 system, so would a course of Flourish Excel help?
Also, I had a browse around looking into some research on Rhodophyta but didn't come across a lot that resembled mine (not that that means much), are you able to further clarify the family/genus you believe it to be?
RODOPHYTA Type 2
This algae is related to an imbalance where where there is too much Ca in relation to Mg and there is an excess of Fe too. Cut your iron to 1/3 of what you have been dosing. Make sure you dont have a lot of 'free' iron (rust)in your tap water. Add a filter for rust and sediment removal if you do.
You can inject hydrogen peroxide just over the algae with a syringe at this rate: 10 ml/25 gallon once a day.(turn off filter and powerheads while doing this) Excel can be use too.
Change the Ca:Mg ratio slowly to at least 50/50.
Algae? Iron Deficiency? Argh! 
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