https://badmanstropicalfish.com/articles/article64.html
A very long article on "Over Engineered Reverse Flow Under Gravel Filter Systems" I finally found a version of it.
Cliff Notes: Layer bottom to top: UG filter plate, floss/filter media, eggcrate light diffuser, floss, eggcrate, window screen, laminate of gravel. Powerheads (I use penguin reverse flow 1140 x 3, 300g/hr each). It pushes the water up in water column (not down like most UG) ie down the tubes, up through the gravel, and traps the crap in the pre-filters on the 1140s. So I don't have to vacuum the gravel. Just change out the pre-filters 1 x per month. Done. Ohh and feed the dudes. Necessary.
This is for fresh water. He references an article that I read 20 years ago and implemented when I built my man cave and put a 125g in a wall. I haven't posted all the information because I knew it was going to take a lot of time.
Bottom Line: Using this system, I haven't cleaned my tank for +10 years. It is a self sustaining "pond" ecosystem. I do water changes, a bit to keep the water level up, change out my filters monthly, and feed. I don't vacuum, nothing. I check the water parameters 4x year and haven't had a fish die from disease in a long time. There has not been any meaningful variance in chemical values at all. Just have to feed the darn animals....sucks!
As an aquarist, my needs are simple: a moving painting, low maintenance. That is it. A center piece in my basement to where people and more importantly, clients, are intrigued by the moving art and puts them at ease. Also for my piece of mind and fun as a hobbyist. It is fun, knowing that I provide an environment to further lives...fish lives. I guess, in the covid state, mental health too.
I assume, if you have tapped into this thread, you understand the basics of fish husbandry: bio load, ph, nitrates, gH, water changes, filtration, water turnover ratios etc. Also, we create a "world" for animals to live in. Totally dependent on us. The fish are not idiots, they interact with people. Heck they chase my laser pointer just like my cats and dogs do.
Because the time it takes to set the system in place, it it not recommended for less then 55g nor a small beta tank
The time spent to set it up, will pay off over time though, for a serious aquarist. I don't care what the Jewish Rabbi thinks.
I am not going to go into the benefits of the HUGE advantages that a UG filter provides over external filters. I have 24 ft sq of biological filtration. This allows me a ton of bio load ability and, hate to say it, neglect. (see low maintenance from above).
One of the down falls of UG, is for digger fish (cichlids), plants and rocks. Because of the egg crates, floss and screen, it is self contained. The gravel is a veneer for them to play with and move around. Not critical in making "holes" in the filtration.
You can have plants, in pots, on top of the substrate. I cut 2 liter bottles in half, drilled holes in the sides for circulation, tossed in some gravel and the plants. I love cichlids but destroy plants. The only ones that worked were: Anubias, Java Fern, and Anacharis.
Rocks create dead space underneath them because water can't circulate which creates ammonia, dead zone. With the lattice of egg crates and floss, this isn't a problem. I have 300 lbs of rock and hiding holes, Mbuna environment, for them to feel comfortable.
As the article mentions, I don't rely on just one filtration system. I have 2 Marineland hang on the back 400's. I just upgraded to 450 pros. Wow.
Fish like to play, so I put in a "water slide", a pond pump that circulates the water (current) that they can play in.
So, in conclusion, I can have 17' of fish in a 125g tank that will be "over crowded", because of the filtration that the Over Engineered Reverse Flow Under Gravel System provides. With all the pumps, I turn the water over 24x hour (4-10x is normal). The 24 ft sq bio filter that the UG provides, I can have a bunch of fish, at VERY low maintenance.
My moving picture will be even more artsy and fun.
I have a bunch more thoughts, but this post is long enough.
BTW, I re-did my tank, total renovation down to the glass, not done in 20 years, and added: Gold Severm, Acei, Tiger Oscar, Blood Parrot, Johanni, Auratus cichlids. On order: Frontosa, Flowerhorn, Green Terror, Yellow Labs, Electric Blue Acara and Rusty's.
It is going to be a busy tank.