plebian
Fish Fanatic
I’ve always had an appreciation for the elegant simplicity of under gravel filters (UGF). I used under gravel filters on my first two aquariums with great success. I owned both aquariums for two plus years each and never had a sick fish or cloudy water. After breaking them down, yes there was an accumulation of mulm under the filter plates, but not so much as to impede the flow of water.When I decided I wanted another aquarium about two years ago I planned on using under gravel filtration again. Unfortunately, where I live the only UGFs available are designed for small aquariums of 20 gallons or less. Since my aquarium holds 180 gallons net and is 9 feet long, I had to go another route.
I ended up purchasing two canister filters, each rated at 1000 liters/hour. Since my tank holds approximately 600 liters net, I thought those would be perfectly adequate. I didn’t realize at the time how much less water flow there would actually be once installed, nor did I realize that filter media capacity would be wholly inadequate for proper filtration. After 6 months of operation, I decided I needed to upgrade to larger canisters.
I replaced both canister filters with filters rated at 1400 liters/hour. In addition to greater water flow, the new canisters also provided a 20% increase in filter media capacity. I fully expected the new canisters to do their job. This time around I performed some real world tests before actually installing the new filters. I was surprised to find that filter media had very little impact on water flow. Most of the reduction in water flow was due to the height to which it had to be pumped, which is reasonable when you think about it. I was somewhat disappointed to discover that the real world flow rate would only be about 600 liters/hour given the height of my aquarium. Still, I thought this would be adequate.
Six months later I was upgrading the canister filters again. This time I replaced the existing filters with filters rated at 2000 liters/hour with an additional 25% increase in filter media capacity. This upgrade had more to do with filter media capacity that water flow. It remains a mystery to me why manufacturers stress flow rates over media capacity, since the latter is so much more important.
In any case, once the filters became established, I finally achieved the level of water quality I was expecting. Unfortunately, a short time afterwards one of the canisters developed a leak. I woke up one morning to find the aquarium had lost about 20% of its volume. It could have been worse. I was fortunate to have tile floors instead of wood or carpeted floors. I decided to revisit the possibility of replacing the canister filters with UGFs, since UGFs cannot leak.
After some research, I discovered it was possible to assemble a larger filter plate from sectional components designed to be assembled according to need. Unfortunately, further research revealed that the design of these components would result in a very inefficient final product. I decided if I wanted a proper UGF I would need to fabricate it myself.
I purchased some acrylic sheets and some PVC pipe and went to work. I’ve attached a photo of the final product.
I decided I would build two filter plates, each approximately 17” x 34”. I would place one at each end of the aquarium leaving a roughly equal amount of unfiltered space between them. This gives me the flexibility to replace the filters one at a time so as to minimize the impact on biofiltration, should I ever decide to do so.
To maximize the effectiveness of any UGF, you need to minimize the size of the gravel you place on top of it. The smallest I was able to make the slots in the filter plate was 2 millimeters, so any gravel used would have to be larger than that. Unfortunately, the gravel I had populated my aquarium with was 2-2.5 millimeters in size so I had to replace it with slightly larger gravel (3-5 millimeters).
I installed the UGFs one at a time, several weeks apart, to assure the gravel hosted sufficiently large numbers of bacteria to accommodate the existing bioload. In my previous aquariums, I used air pumps to power the lift tubes on the filter plates. Air pumps are relatively noisy, and I don’t really care for bubbles, so I decided to use power heads on my UGFs.
The downside with power heads is that only the largest capacity pumps come with duck bill style diffusers to direct water flow. I have no idea why this is so, since being able to direct water flow is crucial in most aquariums. Fortunately, I was able to use the duck bill diffusers from my canisters. They were not a perfect fit, but close enough that I was able to silicone them to the outlets on the power heads.
The power heads I used for the UGFs are rated at 900 liters/hour. Their actual output is equal to, if not greater than the output from the 2000 liter/hour canisters I had been using. As an aside, power consumption has been cut in half.
I expected to have to wait several weeks, if not months, for the first UGF to acquire the necessary bacteria to produce crystal clear water. It only took one week. I assumed this was because the one remaining canister filter had picked up the slack, but that was not the case. Two days after replacing the last canister, the UGFs were producing crystal clear water.
I have come across several sources reporting UGFs functioning for many years without any gravel vacuuming. I believe these sources to be reliable, so I’m going let things go and see what happens. Worst case scenario, I have to vacuum the gravel periodically, something I had to do anyway when using canister filters.
So far, so good. I have not vacuumed the gravel over the first UGF I installed for more than 3 weeks and there has been no noticeable accumulation of detritus whatsoever.
