Hiya,
I've just done one for my 150g tank
I made a faceboard (howto explain) , err, ok, about 1"x6" box around the top edges of the tank, to allow this to sit just lower than full water level i used small square pine pinned/glued from the inside
So the small square pine actually rests on the very top edges of the glass
At the top of the faceboarding i did the same so some ply could sit on as a lid
Between the now ply top and pine that holds the faceboarding on i added some struts across and used some terry light clips (metal stainless steel ones) to hold T5's
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Very simple as i needed a working light system fast, i can lift the ply top off, then pull apart 2 three pin mains connectors and lift the whole thing off, this is a pain on my own, not because of weight, because i'm anal about marking the tank with the power leads that hand from the back of the tank (the power mains for the T5 ballasts)
So i clean the tank with just the play off and alternate which lights are on, i take my time so no biggy really
If i want to go to town on the tank i get a foldaway set of steps out and remove the hood myself or wait for 'her who has to be obeyed' to help me (the ply i used for the top weighs way more than the canopy with ballasts/tubes lol)
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Now this is what i will eventually do (ohh i had plants that were suffering hence i needed lighting asap) .................
Make the faceboarding, same idea of it sitting ontop of the glass with square lengths of wood, same again for the ply to rest on as the top, BUT, the light system i will hinge as a seperate item so i can remove the ply, lift the whole light system up towards the rear (wall in this case) so i end up with a totally open area over the tank surface
The top ply though, i will piano hinge (those long brass hinges) down the centre long length of it, this will make it easier to lift off and store while messing in the tank
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Now to top it all !!!!!!!!!!!!!!!! pffffffffffffffffff
'She' now says, why didn't i use those nice stainless steel wire hangers i have, and make it so it will lower/rise by pulley or motor !!!!!!!!!!!!! (why the heck tell me this months after i asked, dang woman he he)
Also, a variant would be to have a faceboard system nice and tight that will stay in situ, then make lid/lights hinged
Really i learned from doing a quick job, but for now i can live with it but i've put my setup down as a prototype
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With hindsight obviously

i would of put my plants into my moms rio tank and really sat down and thought things through, but hindsight's a wonderful thing
So, just imagine how you need to get into the tank (is that a 6x2x2 ? looks the same as my one he he) For sure i would try and get an overhanging light system made up, or deffo go for a hinged/removable light system/top
Even though my faceboards only raise the tank height by 4" i sure find it slightly easier to reach inside to clean with the whole canopy removed
Can take some quick snaps on the phone if you like, as i say i'm calling this my 'prototype' lol
Tony