I think I know what most people will say... But I still see it as theoretically possible...
I want to create a system using undergravel filters that can run indefinitely. My idea is that by having the substrate heavily rooted in multiple layers (a top layer of shallow rooted plants like Narrow Leaf Micro Sword (Lilaeopsis mauritania) and a deep layer of heavy root feeders like Amazon Swords (and other species), the plants will absorb the nutrients that build up in the soil.
Also, the soil would be something like lava rocks- something known to have a high surface area and is known to be beneficial for plants.
I've had UGF running for years when I started. If we wanted plants we put disks under them to stop the flow through that part of the filter. Plants didn't fair well otherwise.
While something may sound great in theory the only thing that counts is reality.
Well... I could potentially lose everything more evolved than a plant... lol...
Like, please help me identify the problem so I can think of ways to attack the problem. The problem is the buildup of what in the soil? Nitrates? Mulm? What else?
My first larger tank had an UGF. Worked great. I made sure that there was an aria always open in the tank that was about 25% of the bottom which I vacuumed about once a month. Water flow is IMO the key to operating an UGF. It is a bio-filter. It can't get Oxygen to the bacteria nor the water to those bacteria to clean it if there is no flow.
The discharge tubes(frequently one in each of the back corners) will have free flowing bubbles in them if the filter is not clogged. I built my own UGF and added a baffle mid
way front to back so each end would operate separately.
Basically they were invented before people started putting plants in tanks. The people who had them(successfully) knew they needed to be vacuumed.
I don't know about indefinitely, but I know you can do it for 6.5+ years. I set up my 30 gallon in December of 2009. It has full UGF covered with about 3" of montmorillonite clay along with a Marineland C-220 filter to increase circulation and remove larger pieces of detritis. I use a DIY fixture with 2X36 watt 6700K power compact bulbs running in a AH Supply 2X36 watt Bright Light kit. It is covered with a glass top; yes, it has CO2. I do 50% water changes weekly and dose EI along with Flourish Comprehensive and Excel.
Here it was on 12/3/09
On 1/14/10
On 7/7/10
On 2/6/14
And today. I did a very heavy trim on it two weeks ago, thinned and re-planted the Marsilea minuta and Crytocoryne wendtii 'Bronze' (the roots of crypts and swords will go under the UGF but not an issue) and thinned the 'Trident' and trimmed down all of the stem plants including the Limnophila aromatica, Persicaria sp. 'Kawagoeanum', and Ludwigia repens X arcuata.
If you have a lot of rooted plants then an undergravel filter is not necessary at all. An undergravel filter should not be used in the same way it would be so in a fish only tank. Delve some more into the processes that take place within in the substrate.
Is funny. When I first got my 75 a million years ago, I went with a UGF with visijets (the fancy ones with flow meters and stuff). Had a lush growth of sword plants. I looked under the tank once and the roots were all over the bottom of the tank (under the plates). No co2 (before pressurized was ever a "thing" and the info on DIY was scant), and minimum fertilizers (had to use an iron supplement, the flora pride may or may not have been of any use).
Of course THEN UGFs were easy to find. I saw one recently in a local pet store. I was almost tempted to check it for dust.
A reverse flow under gravel filter works great, and lasts for a long time with no maintenance. It also helps prevent roots from growing into the filter slots/holes. I used them for 2-3 years and found nothing to dislike about them. I had the best success when I used a canister filter too, with the filter output going into the under gravel filter. My water was crystal clear. http://www.plantedtank.net/forums/showthread.php?t=78505&highlight=
I saw a method a few years ago that involved a smaller UFG across the front of the tank, then a divider for the substrate, and the rest of the tank was plant substrate. It would involve a little bit of plumbing to direct the water that way, but it looked pretty nice- a band of fine gravel in the front was really easy to keep clean.
It's great to hear so many success stories with undergravel filters. I thought I'd have the constant, lingering possibility that 1-2 years from now, everything in my tank dies one night because the crap collecting in the substrate crossed some tipping point, throwing the water parameters all out of wack. But I think cleaning/redoing the tank once every 6 years is more than reasonable. I'd probably do one every year or so.
I'm thinking that by adding earthworms (who will digest the buildup and maintain it as soil), in conjunction with the beneficial bacteria, and what the roots of the plants extract, there won't be a need to ever clean the soil. Does that sound plausible?
I think one of the major reasons for the longevity of my set-up is the weekly 50% water changes.
Unfortunately earthworms are terrestrial, not aquatic, and cannot live underwater for any duration of time. I do use various species of Corydoras to keep the substrate "clean" along with one Siamese Algae Eater (SAE/not Chinese) and one Otocinclus per 5-10 gallons as cleaning crew.
The main concept of using UGF is that a lot of water flows through the substrate, and this brings plenty of oxygen and ammonia to the beneficial bacteria that live deeper in the substrate than in a non-UGF tank.
As the debris builds up the flow slows, eventually reaching the point where there is not enough oxygen to support the nitrifying bacteria.
That would be true in a fish only tank or a tank with floating plants only. But, a tank with many rooted plants solves the problem of getting oxygen into the substrate. As you know rooted plants transport oxygen via their roots into the substrate.
Yeah, I guess I'll be poking sticks into the substrate every now and then. I did that for my 1 gallon kimchi container 'tank' and it improved the volume of filtered water.
Well, I think the UGF itself would bring oxygen to the substrate. That, and worms, malaysian trumpet snails.
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