# Frogs & Toads > Dart Frogs (Dendrobatidae) > Beginner Discussion >  Curious about fog on glass

## Katieasaur

What ways do you guys think are the best to keep the fog off of your glass? Fans, vents...?

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## Don

Having it vented on top of the fogged glass helps but having vents at top and lower works even better.

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## John Clare

A vent above and below is the best, as Don says.  In my large terribilis tank (see FrogTV), there is only 1 vent, but it's a 2 inch vent running above the whole length of the front glass of the tank as part of the lid.  This is possible because the terrarium has a misting system.  The glass stays fog-free 90% of the time and only gets a bit foggy when it's particularly cold in the room versus the terrarium (it has a heat cable in it to stop it getting too cold in the winter, and this evaporates water).

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## Katieasaur

Well I can put on on top, but it is a 4 foot long tank so how do you vent the bottom?

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## John Clare

You can't without drilling it.  For a large tank like I described you don't need a bottom vent, provided the top one is not narrow.

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## Katieasaur

so I'll just put a 2-3 inch screen vent on the front and cut the glass lid down

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## John Clare

That's what I did for my 40 breeder.

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## Katieasaur

awesomeee thanks so much

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