Algae Removal From A 3D Background

[Smelliot]

I've got what I believe to be hair grass algae all over my 3D wall it's not easy to get rid of I tell you. Last time I removed it was with the high pressure hose however that took off paint too and consequently doesn't look as great. I've tried algae treatments and leaving it in the dark as per say and weekly 50% water changes.
 
- Is there anything else I can do besides bleach it?

 

[DevotedToDiscus]

Can you remove it from the tank? If so one simple solution is to stand it in a window where it will be in direct sunlight. It will dry out, die and be bleached by the sun in a couple of days(weather permitting), and it should be very easy to brush off. 

 

[Smelliot]

Sadly not I got the tank second hand a few years ago for a steal! However the person whom glued the background on put probably a whole tube or so of silicon onto the back of it it's ridiculous. I've even contemplated removing it completely.