Does more flow = more bio filtration?

I'm a firm believer in the fact that slower flow equals more contact time. If you're pushing water too fast through bio, it doesn't have enough time to break down the ammonia efficiently. I believe there is a happy medium


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I'm not sure if this applies but I know for bio-wheels the amount of speed in which the wheel is spinning will not change how much ammonia is being removed from the tank. So whether its contact time with water is short or long, there is not a significant difference. Hope this helps.

bro said:

Okay, I'm going to throw a question out here for debate.

I am pushing 2000 gallons per hour through the wet-dry on my 400 gallon tank.

If I were to increase the flow to say 3500 gallons an hour, will I get more biofiltration, or does the rule of diminishing returns take over. In other words can the beneficial bacteria filter waste faster with More flow, or does it really not matter the flow rate because the bacteria surface area is the same no matter what flow?

Keep in mind I am only talking about biofiltration and not mechanical or chemical filtration

I welcome your thoughts or experiences.

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It depends on the filter and media used. In your case, no, it won't help. Wet/dry has a drip tray to control/slow down the water flow thru the bio media, so in crease the flow may only flood your house.

Hello; My take has been that you can get beneficial bacteria (bb) to break down the ammonia with no flow at all. Some 50 years ago tanks were sometimes run with no mechanical filtration at all. I did a few that way. For a few decades I ran a lot of tanks with filtration only from various forms of air bubble operated devices.
The bb will colonize many surfaces of the tank. These colonies are not going to be restricted to only the active parts of a filter system, they will establish in other places as well. A dynamic balance is established between the bb population and the ammonia present regardless of the flow of water.

I like to think of it in terms of volume, the more water you can turn over the better, but volume of water doesn't mean speed of flow. So if you could somehow move large volumes of water slowly, that would be ideal, like a waterfall vs. a fire hose sort of thing. However, I think flow is beneficial inside the tank to eliminate dead spots and bring the water to the filter, and that's why i like powerheads inside the tank that move water.

Having said that, i'd aim at 4000 GPH on your tank.

I don't know of any specific studies that provide an answer to this, but I'm of the slow flow thought set. my sump runs about 500GPH, around 2x an hour.
ever stand in a high wind? it can take an effort to breath, I can't imagine how much more difficult it would be try and collect food in a similar situation.

I dont have any proof or anything like that, but ive always ran quite a lot of flow and never had any issues with bio. On my last tank with a sump, the tabk volume was 500g and I had a 100g sump with water level at half. I ran a 5500gph pump wide open to get 10x turnover in the system, but the water moving through the sump was turned over about 100x an hour

Hello; My take is that if some volume of flow is too much for the bb to handle, then they will colonize in an area of reduced flow. My guess is the flow rate will be fairly high before the bb cannot function.
From my experience with bubbler powered filter setups having very meager flow, it seems clear that low flow does work quite well. It seems likely that a steady movement of the water is all that is required. Adequate biological filtration can be had with a sponge filter of just an air stone.
Overstocked tanks with lots of bio-load seem more likely to benefit from strong flow.

To be more specific about the initial question, I do feel there is a point of water flow above which there is no advantage gained in terms of biological filtration. I also suspect that flow rate to be fairly low.

IMO, flow is less important than providing the actual surface area for the bacteria to grow on.

Large public aquariums and many large heavily stocked ponds have turnover of just 1 x per hour and their filtration handles the bio-load without a problem. I took a behind the scenes tour of the big 100,000 gallon Amazon Display at Steinhart in San Francisco and the guy said that they run 1x per hour on it. They have enormous sand filters, the size of a car. If they went with the recommendations of 10x per hour, they would have to push 1 million GPH. They don't do anywhere near this and the water parameters are good. This is not a lightly stocked tank either (they have huge Pimas, RTC, Nigers, Pacu, Tarpon, etc). I think surface area is more important than turnover rate.

I'm not suggesting that more flow will hurt, but rather that I'm not sure that it will help from a strictly biological filtration perspective.