Plexiglass tank cover

[jwd007]

Help..I'm getting way too much evaporation out of our 90 gallon. Can I make a cover from plexiglass or should it be glass? Will the plexi distort the lighting? My hubbie and I are in a debate on this issue, all oppinions are appreciated!

[rickh]

The biggest problem is that the Plexiglas will warp and not lay flat. Tempered glass is the best. Why not just buy an AGA versa cover?? R

[polcat_4u]

How much is too much on a 90? Mine goes through 1.5 gallons per day.

[sean48183]

It depends on the type of lighting. If you are running metal halides it will warp. Virtually everyother type of lighting is fine. I use plexiglass for my light covers and I prefer it to glass because it is easier to remove and clean.

[Acrylics]

Acrylic will warp no matter what lighting you use, the warpage is due to moisture absorption in the material. It'll always warp so that the convex side is down, that side (water side) will expand as it absorbs water. Does the same whether you use MH, VHO, T5, or no lighting at all. Either A) just flip that piece over every time it warps or B) use glass instead.
As for distorting the lighting, this is nothing to be concerned with - just kep the piece clean of salt creep - whether glass or acrylic.

HTH,
James

[jwd007]

Thanks, all of you. Our tank looses almost 2 gallons a day. That may not sound like much, but its enough to bring the water level down in the sump so that things don't run properly. So EVERY DAY we are having to add water. It just a small pain, but a pain none the less. I think I will use 3" acrilic across the back and 13" of glass to the front. That way I can create space in the back for hoses, cords etc(plexiglass cuts alot easier). Its great to have a place like this to get advise! Thanks for taking the time!

[rustybucket145]

Sounds like you guys need a larger return chamber in the sump. I have lost as much as 5gal a day during the summer months.

[douggiestyle]

imo the return in the pump should never be enough to flood the tank in case of a clogged overflow. so that needs to be a factor in designing a sump

[flyyyguy]

You dont want to cover your tank with anything solid glass or acrylic. it will interfere with gas exchange.

You should look into a automatic top off device

[mc-cro]

evap is good....,

I agree, dont cover your main tank, you need the gas exchange.

Plus, there is alot of research on glass blocking out some light, especially the thick green stuff.

look into some type of top off designs, then you can think about topping off with kalk water, but they may be a little low on your priorities right now.

[sean48183]

Acrylics- I have had a peice of acrylic that is 20" long by 6" wide over my fuge and under my 2 27 watt compact fluerescent bulbs for over a year and it has not warped at all. Heat bends the acrylic not water. I had a metal halide on my first tank and it bent the acrylic in a week.

[Tang Salad]

I'm also a little surprised at what Acrylics said above. It just seems hard to believe (I'm certainly no expert) that water absorbtion would be the reason for warping. When a sheet is placed horizontally, as above, IMHO two factors would cause it to warp: heat from lights and gravity pulling the center down.

But, again, and in deference to Acrylic's username, let's wait and see what he says.

[flyyyguy]

Originally posted by polcat_4u
How much is too much on a 90? Mine goes through 1.5 gallons per day.

AS long as it isnt leaking and you can control your tank temp i dont think there really is such a thing as "too much". Its just soemthing you have to deal with

I lose 4 on my 90 and about 8 on my 225 a day. I have a ton of surface agitation and MH though.

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im ALSO curious as to James answer on the acrylic water absorbtion thing

Im willing to bet he has a good one though.

[rickh]

I have an acrylic cover on a 10 gallon refugium, about 10x20". It is supported on all sides, there is no light shining on it. It is warped about 3/8". I also used acrylic baffles in my glass sump. They are not warped, but both sides of the material are exposed to the water. It will warp if you use it for a cover. R

[Acrylics]

Hmm, okay...Acrylic is porous, and absorbs moisture. As it absorbs water, it grows. The air gap in the tank that you are covering is a very humid area. Since the underside of the cover is exposed to this, it will absorb water and grow. The top side will be dried out by ambient air, it'll be dried out rapidly by heat from lighting. So, the underside will grow, the top side will not, this will cause the underside to become convex as it grows - almost always. The few times it doesn't warp as much is (usually) if it is in a fish room where ambient humidity is very high and moiture absorption will be similar on either side.

It is very common for many to use Lexan or other polycarbonate (or even PETG) and call it acrylic. Many folks call any clear plastic Plexiglass which is not necessarliy the case. Some plastics such as polycarbonate do not warp as much due to the moist conditions.
BTW, I never said heat wasn't a factor as it certainly is, but the material can warp with or without it. Gravity can be a factor but not nearly as much IME.

Make sense?
James

[mc-cro]

ok, but now help me understand this:

If a tank is made from acylic, what keeps it from bowing?

[MayoBoy]

Is your sump covered? If not, you might look into covering it first and see if that gets you down to a more acceptable evap. rate.

[douggiestyle]

acrylic tank does bow.

james is abolutely correct. ive expeienced it first hand. have a 10g mix tank and i put a plexiglass lid on it so the water would not evaporate. in a few hours it was bowed. there was no heat no lighting only moisture. if you do some research you will find this to be a known and documented fact. some acrylics are less hydrophilic than others. and also as james mentioned pc and others acrylic like materials are less hydrophilic than acrylic.

[BeanAnimal]

Originally posted by douggiestyle
imo the return in the pump should never be enough to flood the tank in case of a clogged overflow. so that needs to be a factor in designing a sump

I prefer to have a HUGE sump with enough evap room to last for a week or more. I build the overflow system so thtat it can not become clogged

In any case it sounds like this setup needs an ATO. The tank cover will cut down a substantial amount of light from the tank.

[BeanAnimal]

Originally posted by sean48183
Acrylics- I have had a peice of acrylic that is 20" long by 6" wide over my fuge and under my 2 27 watt compact fluerescent bulbs for over a year and it has not warped at all. Heat bends the acrylic not water. I had a metal halide on my first tank and it bent the acrylic in a week.

Heat can certainly cause the material to bow, but what Acrylics said is 100% correct. The Acrylic will absorb moisture and expand. The lighted side will not absorb moisture. Hotter lights like metal halides will make the effect more lopsided by keeping hte upper surface 100% dry and hot.

[BeanAnimal]

Originally posted by Tang Salad
I'm also a little surprised at what Acrylics said above. It just seems hard to believe (I'm certainly no expert) that water absorbtion would be the reason for warping. When a sheet is placed horizontally, as above, IMHO two factors would cause it to warp: heat from lights and gravity pulling the center down.

But, again, and in deference to Acrylic's username, let's wait and see what he says.

I am not sure why it is hard to believe? Wood behaves the same exact way. Acryic is a porous substance that will absorb some water and swell. You may be interested to know that most materials will absorb some amount of water.

Reading the last posts by James (acrylics) and douggie should have cleared up any confusion. For further reading, I suggest looking up the words hydrophobic and hydrophillic as they related to polymers

[douggiestyle]

Originally posted by BeanAnimal
I prefer to have a HUGE sump with enough evap room to last for a week or more. I build the overflow system so thtat it can not become clogged

thatll work also.