MH lighting and glass tops

[jcesl2]

I'm trying to find information on this and can't. It seems like its understood that you shouldn't use glass tops with a MH system. I'm not sure why, and what the downside would be.

Right now I just have a shop light sitting on top of my 90 gallon. I will be getting a canopy, and was planning a MH/PC retro kit in it. But I was going to keep the glass tops to prevent fish from jumping, and help prevent evaporation.

Thanks for any help.

[Korwen]

Well, you can use them, but there's a couple reason people don't, and a couple reasons people do.

They do help with evaporation. This means you have to fill up the tank less, as we know the intense lighting required will make water evap quickly. However, they also make cooling more difficult, and make the water hotter. I probably will not use one, because I'd rather not buy a chiller, but just keep some top off water handy.

[apophis924]

The downside of using a glass top with a MH system is heat build up. Glass is notorious for letting in heat and holding it in, which is why green houses retain heat so well. The glass Top would also prevent evaporation which would add to the the total heat of your tank, Evaporation for a reef tank is a good thing it allows one to replace the evaporated water with Kalkwasser which by its very nautre adds inonically balanced Ca++ and Alkalinity in the correct proportions. You might want to try egg crate or some other type of [lastic or PVC screening to keep the fish from jumping out and also allow as much light as possible in and not hinder evaporation. HTH

[jcesl2]

Thanks for the replies. So having a glass top doesn't block out any light?

And I have been looking at HQI lights. These are supposed to have a lot less heat. Would that cancel out the heat issues with having a top?

Final question, if I made some type of screen to cover the tank, it would need to be clear correct? Does anyone sell prefab screens?

thanx

[jcesl2]

Oh, as far as evaporation goes, my sump evaporates about half a gallon a day as it is. Thats why I don't want to have any more evaporation loss.

[aquariumclown]

Originally posted by jcesl2
Thanks for the replies. So having a glass top doesn't block out any light?

And I have been looking at HQI lights. These are supposed to have a lot less heat. Would that cancel out the heat issues with having a top?

Final question, if I made some type of screen to cover the tank, it would need to be clear correct? Does anyone sell prefab screens?

thanx

It will block out light if not cleaned over time. Salt build up that encrusts on the glass blocks the light.

HQI (or double ended MH) are less heat but not enough to make any difference overall.

Personally I think screens will block too much light, so yes, all things considered you ought to have clear covering. Anything plastic will melt, even cast acrylic tops of acrylic tanks warp due to MH heat.

HTH

Leo

[jcesl2]

ok, now i have to figure out what i want to do. thanx

[bler]

I have a 125 with three 'tops'... I plan on using a piece of glass for the middle one and leaving the other two open (prettymuch to keep water from possibly splashing up on the 400W MH bulb (witch I've heard will cause the bulb to explode)..

I plan on regularly cleaning the glass as well..