Dr. Novak, you clearly have demonstrated that my knowledge of aquatic biosphere is lacking to say the least. Anyways are you implying that an under gravel substrate filter system works better than just adding rocks without water circulating thru the under gravel? So a pro head system is better or just an area that is open, like a plenum under the gravel?

Question: Dr. Novak, you clearly have demonstrated that my knowledge of aquatic biosphere is lacking to say the least. Anyways are you implying that an under gravel substrate filter system works better than just adding rocks without water circulating thru the under gravel? So a pro head system is better or just an area that is open, like a plenum under the gravel?

Okay, good question, but for me to answer this one we will have to go back into time to 1960. About this time UG filters came into the aquarium hobby and hobbyist began to realize that their gravel substrate was an excellent bacteria growth media. The lift tubes were no more than 3/8 in diameter, short, very noisy from big air bubbles going through them and moved very little water through the substrate. The UG plates slot were all the same size and water moved through the UG faster closest by the lift tube and a lot slower further from the lift tubes.

What they had in a round-about-way was a plenum and didn’t realize it. Water moves very slowly through a plenum through a diffusion of ions that are negative and positive charged. The water being mostly positive ions in it and the substrate being mostly negative ions and the plenum itself had both positive and negative ions in it. Like a magnet, the positive ions move into the negatively charged substrate where facultative anaerobic bacteria utilize the ions as a foodsource.

Because of the lack of understanding of bacteria growth back them by hobbyist; the UG filter became just that, a new mechanical/biological aerobic filter. Manufactures in their own demise keep improving the UG filter to the point that the water would move faster and faster through the UG plates and brought more oxygenated water with it. Hence, the predominating bacteria became anaerobes instead of the dimorphic facultative bacteria that were in bygone days. By improving with one hand we unknowingly destroyed with the other.

Water like electricity takes the path of least resistance and as clogging encored, water would channel to the easy path of lest resistance. The facultative bacteria lessen and with that left the ability for the UG filter to use Nitrates as a foodsource. Nitrates began to build up to ungodly levels so now more water changes were needed to get rid of the Nitrates. Plus, the UG became another mechanical filter and like all mechanical filters must be cleaned quite often do to clogging.

It was believed back then that plants needed Nitrates as a foodsource so the hobbyist would add more plant fertilizer in the form of nitrogen tabs. This practice still goes on to this very day. Unknowingly hobbyists still think plants need nitrogen as a main foodsource but they do not, they need ammonia/ammonium ions as a food source not nitrogen.

 Also plants do not like fast moving water going through their root system but a slow steady convection movement of water molecules passing over their root systems. Too slow and the plants will die because of the lack of oxygen and too fast and the plants nutrients are not staying around to be utilized by the root hair system so the plants can flourish like they are suppose to.

Now we come to 2015 and what is known today. When I came up with the Anoxic Filtration System in 1989 my studies showed that facultative bacteria utilize nitrates, ammonia/ammonium and phosphates as a foodsource. Stealing oxygen wherever it can from available ions. It was a better bacterium than just using anaerobes alone as thought.

However, facultative bacteria like a low oxygen substrate of 2-.5 ppm (anoxic conditions) of oxygen and not the kind hobbyist provide by moving water too fast through the substrates with lots of oxygen impregnated in it that favors anaerobic bacteria. Anaerobic bacteria make waste that another bacteria now must utilize as a foodsource. If this balancing act is disrupted in anyway, the system will fail and cyanobacteria and algae will be the outcome.

So to answer your question. Lift the gravel off the bottom of the glass with a plenum and utilize the same reaction action as a natural system does. Natural systems move water in and out of their substrate slowly through electrical charge like an AFS does and through convectional movement, percolation and diffusion abound. If you do not do this, then diffusion is interrupted and impedes the oxygen flow into the substrate.