Of Fishless Cycling And The Filter

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Aussie_Dog

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I just have a quick question: I know some filters have a flow level, where you can turn it down for feeding the fish and calming the fish who don't like the fast moving water. But does the cycling process speed up if you turn the flow up to it's maximum? I'm not quite sure how that works, which is why I'm asking here. I'm going to go out and get my tank today (60gal) and, I'll be honest, if there's ANYTHING that could speed up cycling even a little bit, I want to take advantage, lol. But if turning up the filter really doesn't do anything except create noise and splashing, it'd be handy to know, lol
 
The short answer is no. The limiting factors that holds back bacterial growth are ammonia concentration, oxygen availability, temperature, and pH.

The ammonia is effectively food, and the more there is, the more they can grow (up to a point). Oxygen is very important but often ignored. The job of water flow through a filter is primarily to keep the flow of oxygen adequate for the bacterial activity. A canister filter starts to die back within as little as 20-30 minutes of being switched off. The more water flow, the more oxygen is transported through the filter, and the faster the bacteria will multiply.

Temperature is important because bacteria grow faster the warmer it is. Obviously very hot water kills them, but warm water contains less oxygen than cold water, so there's a cut-off point where warming the water actually does more harm than good.

Filter bacteria hate acidic water, and won't work at all below pH 6.

All this said, while increasing the water flow could increase the amount of oxygen passing through the filter will have a beneficial effect, this effect will be slight. Even under the best circumstances it'll take more than a month to cycle an aquarium, and normally around 6 weeks. This is a good time to do things like aquascaping. Plants couldn't care less about ammonia, so spend this time buying plants and decorating the tank.

Cheers, Neale

I just have a quick question: I know some filters have a flow level, where you can turn it down for feeding the fish and calming the fish who don't like the fast moving water. But does the cycling process speed up if you turn the flow up to it's maximum? I'm not quite sure how that works, which is why I'm asking here. I'm going to go out and get my tank today (60gal) and, I'll be honest, if there's ANYTHING that could speed up cycling even a little bit, I want to take advantage, lol. But if turning up the filter really doesn't do anything except create noise and splashing, it'd be handy to know, lol
 
Thanks! I'm starting off with just the tank (and stand) and heater and filter, as well as my trusty bottle of ammonia, and will be buying the rest of the stuff during the cycling process. I already have my eye on some stuff on ebay, lol (especially the silk plants) and am STILL looking for some play sand in my area. Looks like the hardware stores and toy stores don't have it, but maybe that's because it's winter? Here's hoping sandbox season actually exists in springtime, lol. I'm not looking forward to pay some $45 for sand at Petsmart (and it's not even sand, just finely crushed gravel)

Again, thanks!
 
I can't see that fast flow rate actually benefits bacterial growth within filters. The capacity and type of media it holds makes a difference because a bigger surface areas = more space to colonise. Having a high level of oxygenation is important. Having loads of water movement from a fast flow rate will achieve this but then your highly oxygenated water will not be in contact with your media that long because the flow rate is high. This would make it harder for bacteria to absorb it. The opposite I would have thought will also be true ie. a slow flow rate will allow longer contact between the water and the media giving more time for uptake of oxygen. But you will not have a lot of water agitation in this scenario so oxygen levels will be lower.

I would predict, but not with certainty, that greatest bacterial growth would be achieved with a slow flowrate through your filter. Then angle your spray bar to create as much surface agitation as possible. A separate pump could also help with this as would a bubble bar. Combine these changes with your raised temperature and 5ppm ammonia and you will have perfect conditions for fast bacterial growth.

:good:

ps. Getting hold of some ceramic media and sponge from a mature filter can more than halve your fishless cycling time.

edit: having seen what nmonks has wrote and him being far more knowledgeable than me. I would now say that my advice my be wrong. However, I wait to stand corrected ;).
 
I admit it isn't obvious. But it's about transportation of oxygen from the limited supply at the surface of the water to the places its being used. The more the water flows around the tank, the more oxygen is available.

If there's no flow at all, oxygen goes into the water at the surface (diffusion) and then slowly spreads down the tank (more diffusion) and then gets absorbed by the bacteria in the gravel or filter. When you add a water pump, oxygen-rich water is physically carried to the bottom of the tank, and oxygen-poor water is carried to the top. This means you remove the slow diffusion bit in the middle, speeding the whole process up. The bacteria in the filter or gravel get more oxygen per second, so can multiply up to a larger population. The more water flow, the more oxygen is being moved about, and the more the bacteria can multiply.

The diffusion rate at the top of the tank is basically dependent on the concentration of oxygen on either side of the air/water boundary. When the water is still, the oxygen concentration in the surface layer will be relatively high because nothing is using it up and it can easily accept oxygen from the air. In other words, the diffusion gradient is gentle, and the net intake of oxygen will be low. A water pump moves oxygen-poor water to the surface instead. There is a steep diffusion gradient now, because the deoxygenated water has little oxygen while the air has lots. So the rate of diffusion will be faster. The more the pump moves oxygenated water away from the surface and deoxygenated upwards to the surface, the steeper this gradient will be, and the faster the oxygen uptake gets.

It's essentially the same thing as happens in your lungs. Oxygen isn't left to diffuse into the blood from the air and then diffuse around the body. That would be too slow. Instead deoxygenated is pumped to the lungs so that it rapidly accepts oxygen, and oxygenated is pumped away to the rest of your body so that it can supply your tissues. Think of the surface of the water in your tank as the lungs, the pump as the heart, and the water as the blood. It all makes sense now! The faster the pump, the better the circulation of oxygen.

Of course there are limits. Even if you have a super-filter that turned the water over 20 times per hour, filtration would level off at some point because other factors, like ammonia concentration, would become limiting.

Cheers, Neale

I can't see that fast flow rate actually benefits bacterial growth within filters.
 

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