View Full Version : Glass or Acrylic Lid??

Stuart Elflett
20-06-07, 03:52 PM
Ok, I picked up a 60L tank, and it came with one lid, and two halves of the other lid... the light unit may well make the question moot, but seeing as I deal regularly with an Acrylic/Perspex supplier, the choice came to mind - is there any major reason why I'd need glass lids, rather than a good quality 5mm perspex??

I can have the perspex cut to fit, including spacing for airlines, heater and filter cords, etc, for well less than $10 - it's UV resistant, so shouldn't yellow - and if it does, I can replace it in the future... plus it wouldn't be so hard to pop hinges on it so I can lift it up, if the light unit would work within that kind of spacing...

(I'm putting a 2 X 24W T5 unit on the tank, btw, if that'll make heat that may be a concern for acrylic material...)

20-06-07, 03:55 PM
Only a heat issue, but 5mm may be thick enough.

A while ago I had a lid made from acrylic on a 4 footer. The lights were T8's and I did have some issues with the acrylic buckeling, but mine was only 3mm thick.

20-06-07, 04:25 PM
Same here, my homemade acrylic lids bowed terribly.

05-01-09, 09:24 PM
I want to replace my glass lids (which I have never used) with acrylic lids over winter. I need to get a total of 6 lids of equal size 620mm x 240mm. These lids will be directly under 150w Giesemann metal halides (incidentally my Giesemann 260 system seems to give off little heat compared to other metal halides, although mine is an open style set up). My question is should I get these lids cut in 6mm, 8mm or perhaps even 10mm acrylic ?. The aim is that I do not want them to bow at all, even under the heat from the metal halides. I understand that there will be no flex in these 625mm sheets with 6mm acrylic, but that doesnt account for the heat from the metal halides. Opinions appreciated

05-01-09, 09:42 PM
Stingray - why not get glass lids?

05-01-09, 09:57 PM
I have acrylic/ perspex over my tank to stop the fish from jumping out, and they are pretty thick and they all bent. No matter how I tried to put them over the tank.

06-01-09, 03:51 AM
10mm will bend. I have it on my crypt tank only with T8 lights and all the sheets bent.

06-01-09, 08:45 AM
Hey Guys,
Thanks for your responses, all helpful. The reason I want Acrylic lids is that my current Glass lids are very heavy and extremely delicate and flimsy in that size (625mm x 240mm). The lids make a lot of noise when I move them and there is no room for error from a misplaced glass lid, particularly when the tank is over 1000 litres and stands 1.58m tall without a hood. I plan on using the Acrylic lids over Winter to keep the heating bills down (& also to prevent my M boesemani rainbows from jumping out and being eaten by the cat !).

Roughly how long are your 10mm Acrylic lids (just to give me an idea of bowing) ?

How long are those lids and what is the thickness of those lids (once again to give me an idea of bowing) ?

I tried the 6mm glass lids on last night for the first time ever under my Geisemann 150w metal halide unit and they hardly warmed up at all. Perhaps it's the Osram 5700k bulbs that run cool, or the fact that the light unit is suspended 300mm above the tank (as apposed to 200mm), but there was barely any heat on the lglass lids after 5 hours of lighting on a warm day.

06-01-09, 04:02 PM
Roughly how long are your 10mm Acrylic lids (just to give me an idea of bowing) ?

45cm wide by 73cm long

06-01-09, 04:51 PM
I have tried both thick and thin acrylic over the years, acrylic all bends and scratches much more easily glass. I no longer use acrylic.


06-01-09, 05:50 PM
Thanks Guys,
So do you think that thick and thin acrylic bends because of the water absorbtion or is does the heat from the light come into play ?

The only other option then is polycarbonate (lexan). This material apparently has very little water absorbtion and may be up to the task. It costs nearly double the price of acrylic I was told today.

06-01-09, 08:16 PM
What if you use acrylic and then use some other material (stainless steel?) to make a structure to support the lids?

Like....say in an "X" shape to stop it bowing? Does that make sense...?!

Just an idea :)

06-01-09, 09:06 PM
stingray, where abouts are you,
i have some thick glass that could help you out.

07-01-09, 05:58 AM
I think acrylic bends because it is a poor conductor of heat and the warm side expands causing it to bend. Acrylic can be polished, I once spent 10 hours a day for 8 days polishing the inside of the Territory Wildlife Park walk thru tunnel. 3M make a plastic polishing kit called "Finnese It" which works quite well. You just follow the instructions in the little booklet.


07-01-09, 08:01 AM
Micheax thanks for the offer, but I already have 6mm glass lids (6 heavy lids all up) for this tank. I was looking for an alternative that was lighter, safer and more user freindly.

Dave, I have done further research on this in the past few of days (mainly info from other global fish forums) and it appears that the main reason acrylic lids bend is because they absorb quite a bit of water on the side facing the water coloumn. This is the main cause of the warping. Whilst It does appear that the heat from aquarium lights will speed up the warping process, there seems to be some evidence that the warping would occur without any lighting heat whatsoever.

07-01-09, 09:14 PM
get your lids cut again.

im assuming they are like mine,.

small for the front and big on the back,

get the back one cut in half. so you end up with 3 small lids. easy to move etc..

08-01-09, 06:46 AM
The tank is 1830 long x 760 wide x 760 high (6'x30"x30" for the old fashioned).
It has a 250mm centre brace and two 150mm end braces. So there are two sections either side of the centre brace that require lids (over winter). Their are 3 lids for each of these two sections and they run length ways. Each of these lids (6 in total) are 625mm x 240mm. If I was to stick with glass lids, should lids of this size (approx 2 foot long or 625mm) be in 4mm, 5mm or 6mm. I guess people with 2ft wide tanks will be able to answer this if their lids go front to back. The current lids dont quite fit anyway and I need to have some of the recut. Or perhaps I can get the lids redone in 4mm or 5mm to bring down the weight ?