Why Drainage Layers Suck

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There is almost never a good reason to use them —

I dont think there is any aspect of modern herpetoculture quite as ridiculous as the drainage layer. Incorporating a drainage layer in a vivarium is akin to keeping a mop and bucket in your bathroom for those times you overflow the bathtub. Here’s an alternative to that bucket and mop: stop overfilling the bathtub.

Its worse than that though. Drainage layers can cause serious harm, even death to vivarium inhabitants. They promote the growth of bacteria and potentially pathogenic viruses. They promote over watering which is a common cause of water related disease in both reptiles and amphibian, and they have not infrequently trapped and killed vivarium inhabitants under the protective screening.

Misting systems can easily compact the substrate and drive air pockets out, which destroys the bioactivity of the substrate and creates an anaerobic environment that is as stinky as it is dangerous. The mistake of drainage systems, caused by the mistake of misting systems, thus leads to the mistake of compacted, dead substrates. And of course all these mistakes result in the development of expensive, but largely worthless “bioactive substrates” that the bioactive companies offer in spades. Oh what tangled webs we weave!

(Not entirely worthless – See: When and How to Use Mist and Rain Systems)

On top of all that bad, they actually go one step worse by doing absolutely no good. Drainage layers got their start, near as I can tell, by keepers who wanted to compensate for another bad vivarium technology – the misting system. Misting systems can be used to the benefit of the kept, but 9 times out of ten they are over used. The misting systems, in turn, were devised in response to yet another misunderstanding in early dart frog keeping: that very high humidities were “natural” and that this high humidity was best delivered from above via misting. (See: The Humidity Mystery).

So once these early keepers got their misting systems all revved up and saw all the wonderful mist raining down on their tiny tropical vivarium inhabitants they couldn’t control themselves. It was just too cool to use only once a week, which would have saved them a lot of grief in the long term! To this day I hear recommendations of misting vivariums daily. Even multiple times per day – creating an artificial environment that can not be found in nature and that no animal is adapted to. (OK, so I can think of a couple misty highlands that actually do look like modern bioactive fog-fests, but very few of our captive species come from these rare environments – certainly the tropical dart frogs do not.)

So if you are not able to control your misting system, you’ll soon have a paludarium instead of the terrarium you intended. The obvious solution, and the more natural solution, would have been to back off on the misting. I’ve tried to describe elsewhere that in nature humidity comes from the earth, (See: The Great Substrate Debate, and Managing Substrate Moisture) not the sky. The unhelpful paradigm of trying to raise humidity by misting is difficult and even detrimental to the animals’ health. It should stop.

And yet it is common for new keepers, even some seasoned keepers, to reflexively recommend drainage layers (and misting systems) as part of a natural or bioactive set up. I have even read recently where someone has made up the idea that drainage layers facilitate a supposedly important “watering from below” of vivarium plants. This fantasy apparently stems from the practice of watering bedding plants, particularly seedling vegetable plants that easily succumb to stem rot, by filling the trays the pots sit in with water and allowing the water to be absorbed from below. While this is indeed helpful getting your vegetable garden started, it has no purpose in hepetoculture.

In summary, I would suggest that we should never incorporate drainage layers unless there is a specific species need that justifies the cost, complexity, and potential down sides of their use.

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Published by Joe

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