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How To Drill a Glass Aquarium

News From the Arctic – How to Drill a Glass Aquarium

By Erica and Adam Till/ Arctic Lights Aquatics

Hi there folks!

As part of a new blog series that we’ll be writing for The Goldfish Council, the following article will help you address one of the most common issues you’ll face as you start to grow your goldfish collection – how do you manage the work that’s involved in keeping a large number of goldfish?

Some of the easiest ways of doing this are to either add sumps to increase the water volume of your display tanks or to add a water change system to automate changing the water in your fish room tanks. Both of these work well, but both share a common challenge – how do you drill holes in the tanks to allow these upgrades to be installed safely?

The Challenge

If you’re anything like me, the thought of drilling a hole in a perfectly good aquarium isn’t exactly the sort of thing you look forward to. In fact, I was so nervous about the prospect the first time I used a sump that I just paid our local aquarium builder to do it for me; it was $30 well spent!

That said, even at $10 a hole, when we started to setup a 20-tank breeding operation this winter, it quickly became apparent that I couldn’t take each tank up to the builder to get the holes drilled for me. For one thing it was time consuming, and for the other it would start to get expensive.

So armed with a 1 ¾”glass drill bit we bought off Amazon (the size required for a 1” bulkhead) and a complete disregard for violating the warranty on our tanks (drilling a hole will do this understandably), we set out to figure out how to drill an aquarium safely.

The Philosophy

The first thing to realize when you set out to drill an aquarium is that, rather than “drilling” a hole with a twist bit like you would use to put a hole in a wooden 2×4 beam, with glass you’re actually slowly grinding away glass in a circular pattern rather then tearing it off in chunks like with a wood bit.

As a result, unless you make the mistake of trying to drill a tempered glass tank (contact your tank manufacturer to find out if your tank in made of tempered glass) and you’re not trying to drill a thin walled 5 gallon tank as your first victim, odds are you aren’t going to shatter the tank into a million pieces using a glass drill bit.

The Tools

The best tool for drilling a glass aquarium that I’ve found is a simple diamond coated tile hole saw like you can get on Amazon for a few dollars.

Though it’s certainly possible to get more expensive bits, these don’t seem to be significantly worse at a fraction of the cost of top end tools. In a nutshell, these bits might drill 6-8 aquariums, where more expensive ones might drill 8-10 at four to five times the cost.

Next, you’ll need a simple piece of cheap plywood that fits inside the aquarium you’re planning to drill. This sheet will help start the hole, and will prevent the bit from wandering and scratching up the tank.

Lastly, you’ll need a variable speed drill of some fashion. It doesn’t much matter if it’s corded or cordless, but I prefer a cordless just for sake of simplicity.

The Process

The first thing you need to do is to figure out where you’re going to start your hole.

For the most part you can drill any portion of an untempered aquarium, but at minimum try to stay at least an inch from any edge, frame, or any other hole. The lower on the tank you drill, the more pressure will be exerted on the edges of the hole, so try not to put multiple holes in the bottom of an aquarium, close together.

That said, if you are drilling the bottom of an aquarium to grow out ranchu or to drain under an undergravel filter plate, be EXTREMELY careful that the bottom glass isn’t tempered. If any glass panel on an aquarium is going to be, it’s usually the bottom, so check with the manufacturer if you’re not sure.

Once you’ve decided on a location, press your plywood sheet into an inside corner of the tank and mark the location of the hole on the plywood. You remembered to account for the width of the bulkhead flange and it still clears the tank frame, right? Good, just checking.

Next, take the plywood out of the tank and drill a hole through it with your bit to create a drill guide. The wood will likely smoke a little, and you’ll appreciate a thinner piece of plywood rather than a thick one, but the bit itself will be fine. Starting this hole can be a little tricky, but if you tip it at an angle and start the drill slowly you’ll get the hang of it quickly (at least you don’t have to care about cosmetics on the plywood).

When you have your drill guide finished, ideally your tank will be big enough that you can drill from the inside out (that you can fit your drill inside the aquarium). Since the most critical surface from a leak-prevention perspective is the inside, that’s what I prefer to start with. Additionally, most times if you’re drilling from the inside out you won’t have to clamp the plywood in place, which is a nice bonus. If you’re drilling outside-in, hold the drill guide in place with some soft-jawed furniture clamps, and place something inside the aquarium to catch the glass blank that might fall from inside the hole.

For safety (and to contain the mess), I drill my aquariums outside on the lawn. Once you’ve found a spot that works, place an old folded-up towel underneath the tank so that it’s putting pressure on the spot you want to drill. This will support the outside edge of the tank, and help to minimize chipping on the outside edge. Some people try to use tape to do this, but I haven’t found an added benefit using the tape vs using the towel.

In order to keep the bit cool while you’re working you’ll need to provide some water for lubrication. Some people build a small dam using clay to accomplish this, but since I prefer to drill inside out, I just fill the side of the aquarium with water using the rim to hold the water in (obviously not possible with a rimless tank, which might require a helper with a hose to keep water on the bit).

With the aquarium supported and the water bath in place, the only thing left to do is to go forth into the breach and drill! The first few seconds of drilling will be abject terror as you picture the tank shattering into a million pieces (if it’s not tempered, it won’t), the first hole will still have you nervous until the hole is finished (especially as it gets close to the outside), and then you’ll lapse into a bored coma for any subsequent hole (the process quickly becomes pretty routine).

To start the bit, place it firmly against the glass inside the hole you cut in the drill guide. Don’t try to tip the bit to start the hole, but just rely on the guide to keep it from wandering. Start on the slow side if you’re nervous, but once the hole is started, feel free to pour on the power.

Don’t try to use pressure downwards on the drill in order to “help” the bit work faster, and instead rely on the weight of the drill to provide enough drilling pressure. Expect to take around 5 minutes to finish a 20 gallon tank, and to have an aching trigger finger when you’re done (taking breaks is fine, as long as you make sure the drill is lined up properly when you restart the hole).

As the bit approaches the outside, be sure you’re not putting any downward pressure on the drill. The lighter the pressure and the more level the bit is, the less chipping you’ll create as the bit exits the glass. Out of a dozen tanks I’ve drilled lately only one had any significant chipping (I got greedy and used too much pressure), but I haven’t broken a tank and even the chipped one was usable (if the bulkhead seal extends outside of the chipped zone, it’ll still seal properly).

That’s it! Spray out the (very sharp) glass dust with water, give it a wipe with vinegar just to be sure, and you’re ready to install your bulkheads.

A Last Word of Warning

Glass dust isn’t great for your skin, and the edges of the tank and the glass circle you cut out will be sharp, so PLEASE take care in handling all of them.


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