"Turnover" is the number of tank volumes that is run through your filter each hour. If you have a 100g tank and the flow through the filter is 100 gph, then you have one turnover or one turnover per hour (which is actually redundant).
A variation of this is adding up the entire system volume.
I have maintained a well stocked tank with nothing but a powerhead circulating water over the gravel substrate. So by your definition; I have zero (0) turnover?
When it comes to actually determining your turnover rate there is only one surefire method - measure out the time it takes to fill a given volume. You can either use a bucket on which you have marked a level (I like using a 2.5G bucket that I marked at two gallons) or lower the water level in your tank by a certain amount and then calculate the volume. Time how long it takes and then do the math:
3600 ÷ [# of seconds to fill] × [# of gallons filled] = GPH
Any other method will give you an inaccurate figure, there are just too many unknown variables to factor in. Just as an example, a recent DIY filter I built using a Rio 2500 (rated at 782 GPH) has an output of 327 GPH.
I have maintained a well stocked tank with nothing but a powerhead circulating water over the gravel substrate. So by your definition; I have zero (0) turnover?
Yes.
That is to say, if you do not import or export water from the tank to any form of filter or sump and perform all mechanical and bio filtration in the tank then you have ZERO turnover.
You say you have a powerhead circulating water over the gravel substrate so can I assume it is not a UGF ?
What sort of maintenance do you perform ?
I would love to see a pic of your setup.
Chris
I have maintained a well stocked tank with nothing but a powerhead circulating water over the gravel substrate. So by your definition; I have zero (0) turnover?
Yes.
That is to say, if you do not import or export water from the tank to any form of filter or sump and perform all mechanical and bio filtration in the tank then you have ZERO turnover.
You say you have a powerhead circulating water over the gravel substrate so can I assume it is not a UGF ?
What sort of maintenance do you perform ?
I would love to see a pic of your setup.
Chris
My filterless tank was a 26G with pebble substrate that I use as a hospital tank. It already had an occupant (beat up African Cichlid). As I mentioned on another thread, this tank pretty much has been occupied for four years; however, I usually only have one fish in it. So I knew there was an established BB colony in the substrate.
Anyway, I moved 3 more African Cichlids into the tank to thin out the herd in two other tanks. The ACs were between 3 and 4 1/2 inches. BTW - I posted this experience last year in one of the bio-media threads.
The plan was to take them all to the LFS. However, for a few months, my LFS was not accepting any unused fish; so these guys ended up in the "temporary" holding tank for over four months.
I did a 50% WC and gravel vac each week (same as I do for all my tanks). I checked the levels a number of times to see if I needed to invest in a HOB w/ bio-media. To my surprise, the ammonia & nitrite levels remained at zero.
I have maintained a well stocked tank with nothing but a powerhead circulating water over the gravel substrate. So by your definition; I have zero (0) turnover?
The optimal turnover rate is variable from tank to tank. For argument's sake I'm assuming the optimal turnover rate is considered as the optimal minimum turnover necessary to assure good water quality. I consider the five following factors to be most important when calculating turnover;
1 - Type of fish (s**t)
2 - whether air stones or powerheads will also be used
3 - Shape of tank
4 - bioload effects on oxygen
5 - end size of fish
For instance some fish produce waste that stays in midwater while other fish produce waste which sinks faster. If you plan to keep fish which produce "floaty bits" then you need a higher turnover rate to clear the water. If your fish do "sinkers" then the mulm can be much more easily directed to a filter intake lower in the water column. This can be achieved with the judicious use of water current whether from the filter return, a powerhead or air stone.
Problems may also occur with irregular shaped tanks or ponds requiring multiple filter intakes. Often more turnover will be necessary for multiple intakes otherwise the individual intakes won't draw enough water to pick up mulm.
One important variable is oxygen. If you are relying solely on your filter to bring oxygen into the water like with a trickle filter then you will need to adjust the turnover rate so enough oxygen is present for the bioload of the tank. I wouldn't recommend doing this however as you then lack a backup if your filter pump should fail. For that reason I always use an air stone or powerhead in tanks with a high bioload.
For those worried about nitrification with low turnover rates I have filtered systems with a turnover of 4 times a day without problems. However I always used pumps in these system to create water current to direct the mulm to the filter intakes.
Why I prefer a lower turnover is because of saving electricity and because a filter will polish the water better if the flow is slower for a given filter cross section. Obviously these benefits won't be seen if the turnover for the system is below the optimal minimum turnover.
How I determine the optimal minimum turnover for unique systems is unfortunately largely dependent on personal experience. I clasify a unique system as something outside of the standards already developed for aquaculture settings. Since most aquariums on MFK fall into this category it remains up to the individual to experiment with each system to find out what the optimal minimum turnover may be.
As an example my current 6x2x2 has a turnover of 2 times per hour with the fish in my sig. The only other water current comes from air stones. The biggest fish is one of the eel tailed catties at 30cm(12 inch) with 5 other fish over 25cm (10 inch). The water current settings are quite finely tuned though. If you don't want to stuff around so much with water current my recommendation for such a setup would be closer to a turnover of 4 times an hour.
On the other hand I have had success with tanks in the 4 to 5 metre range (13-16 foot long) with a turnover of once an hour due to the lower per liter bioload.
