Home Made Nitrate Filter

[chrismrutherford]

I may have just figured out a way of lowering nitrates in my tank. Having viewed some commercial biological nitrate filters it is clear that to remove nitrates you need anaerobic bacteria. With a normal external canister filter that circulates water from the main tank at a relatively high rate you have too much oxygen for the anaerobic bacteria to thrive.

In order to breed the anaerobic bacteria you need a flow rate low enough to guarantee that your canister filter contains oxygen depleted water. The commercial systems use a drippier to feed the filter with drops of water, where the flow rate is 1 - 4 l/hr ( 0,25 - 1 gph) for a small tank (5 L canister) and 12 - 30 Liter/hr ( 3 - 8 gph) for a large tank (30 L canister).

Building a drippier system is complex but putting a timed relay on a normal canister filter isn't. I set a relay timer circuit to 90 seconds off, 2 seconds on. I measured the flow for one pulse to be 100mL, which averages out at roughly 4 liters per hour. I used a spare AVEX 600 external canister filter with a volume of 2.3 Liters. I replaced some of the filter medium with porous clay pebbles to increase the surface are and encourage bacteria growth inside the pebbles where the oxygen will be at its lowest. I used a Velleman adjustable interval timer placed inside a plastic box with a 12V wall mounted power supply. http/www.vellemanprojects.com/be/en/prod...view/?id=366732

I took some water out of my tank with quite high nitrates and put it in a test tank. I then left in with my anaerobic filter for about 1 month. When i measured the Nitrates they had fallen to zero. I have since connected the filter to my main tank and I'm eagerly awaiting the results.

Has anyone tried this before? Will it work on my main tank? What removed the nitrates from my test tank?

Thanks

Chris R

 

[jgray152]

very interesting. Im just wondering if it would be able to keep up with the beneficial bacteria creating nitrates.

 

[Colonel Mustard]

i supose you could adapt it

 

[Tolak]

That's an interesting way around the low flow needed for a nitrate filter. Sounds similar to the auto feeder a buddy of mine built some time back. It would put out 10ml of bbs, straight from the hatchery, every hour. He did a large water change every evening after work to keep the salt level down.

 

[chriskali]

Sounds good although I would monitor for nitrites, as in some cases nitrate can revert to nitrite.

 

[andywg]

I can see a couple of problems here.

Decent nitrate filters have a redox meter in the filter to measure the oxygen levels and adjust the dosing levels accordingly. Without this nitrate filters tend to crash in the medium term (6 months or so if you are lucky).

Also, if I am reading right, you have it so that the filter pump starts up for a couple of seconds, and then shuts down for 90 seconds? If so then you are on a sure fire way to destroy the pump. Very few pumps in the hobby are designed for continual switching. Those that do are normally run on DC and not AC.

I know CFC looked into nitrate filters before, but the only way he found that might make it work on a tank that was up and running would be with the redox meter connected to a dosing pump. Water changes are far easier (and take care of dissolved organics and the likes as well).

 

[Underwurlde]

Very few pumps in the hobby are designed for continual switching. Those that do are normally run on DC and not AC.

What makes you say that?

 

[dylema]

I would also question the flow in that 2 second burst. If you quickly flood the filter with oxygen rich water every 90s then it would stop the process.

andywg, you know about deep sand beds (DSB) and things of they nature right. is it not possible to use a DSB in a fresh water. so if you used a canister and instead of having water flowing right through it could come in the top be deflected (say a right angle tube) and back out the top with the canister half full of sand. Therfore the water in the bottom of the sand will be quite anoxic and the pump will not be under undue stress.

Dylan

 

[andywg]

Very few pumps in the hobby are designed for continual switching. Those that do are normally run on DC and not AC.

What makes you say that?

The fact that the main ones I am aware of (The Tunze Turbelle pumps) explicitly state not to try running any of their AC pumps on the wavecontrollers as it knackers the pump. It continues to say that the DC pumps are the ones that can be controlled. I have also read other reports where people have found that plugging normal powerheads into powerstrip wave timers seems to shorten the life of the powerheads involved.

I assume it is somewhat similar to light bulbs which only tend to fail on the initial start up as that is the part that places the most pressure on the components.

 

[Underwurlde]

Lightbulbs bust because when you switch them on they are cold and have hugely less resistance to when they are white hot. Lower resistance = higher higher current. Hence the 'weak' time for a light bulb is when you switch it on and get an instantaneous huge in-rush of current. Notice how light bulbs seem to bust when you switch them ON as opposed to when you switch them off (not that you'd know until you try to switch them on again ).

Motors on the other hand would behave differently - due to the inherent inductive design, they actully do the opposite: Motors are wound, they are inductors and inductors 'resist' a change in voltage (i.e. switching) by choking the current. However, AC induction motors (I believe those commonly used in power heads and the such like) need a kick to get them started and they get this from motor start capacitors - capacitors behave in an opposite manner to inductors and actively encourage voltage switching and have a much lower resulting impeadance and much higher in-rush current. It is usually these caps that go pear-shaped, not the motors themselfs - but this is academic because the whole motor assembly is submersed and therefore potted in a hard setting epoxy rendering the repair of these 'motors' (in other words the capacitors) impossible.

Andy

PS
I have made so many assumptions it is unbelieveable and hence I'm probably spouting utter drivel.

 

[The-Wolf]

is it not possible to use a DSB in a fresh water.

I can't see why a DSB, in say a sump, wouldn't work as well in freshwater
as they do in saltwater.
in fact adding a sump with a DSB to my 42G (which has a weir feeding a cannister atm)
is something I'm considering.

 

[andywg]

I would also question the flow in that 2 second burst. If you quickly flood the filter with oxygen rich water every 90s then it would stop the process.

andywg, you know about deep sand beds (DSB) and things of they nature right. is it not possible to use a DSB in a fresh water. so if you used a canister and instead of having water flowing right through it could come in the top be deflected (say a right angle tube) and back out the top with the canister half full of sand. Therfore the water in the bottom of the sand will be quite anoxic and the pump will not be under undue stress.

Dylan

As Wolf said, a DSB should function in FW, and I seem to recall that nmonks knows someone who did a variation of one as a proof of concept.

I seemed to have some luck with a DSB using old Fluval cannisters (until they finally failed, as all fluvals like to) on SW. All I did was have rock work to stop the flow stirring up too much of the sand. I am gradually changing the sump system on my large FW set up to try and get a DSB on that. I now effectively have a spare sump tank as the wet dry trickle tower flows straight onto the tank with the return pump in it.

The concerns expressed with FW set ups of this nature is in the role of micro-fauna. Due to the presence of live rock in salt water tanks you have a number of organisms that will colonise the DSB as well as the bacteria. It is uncertain exactly what role these play and whether they are necessary or not. We don't tend to put anything other than fish in a FW tank, so we are not likely to get these small animals that might help.

 

[dylema]

Thanks for that guys even though its not my thread. I like the idea of using something to reduce nitrates. Perhaps for the sake of the murray (Australians will get that joke) we could work out a FW tank with nitrate reducing filters and Skimmers to help with organics etc and say goodby to daily/weekly water changes.

 

[Tolak]

I was thinking, to get around cycling the motor constantly, couldn't you use an old infusion pump, the ones used in the medical industry for measuring I.V drip rates? I haven't looked into the price, but I'm sure this is something that could be picked up used.

 

[dylema]

Tolak, are they the pumps that have a tube bent around in a U with a cam of sorts that squashes the liquid around the U? If it is what I am thinking of these are also used in commercial dishwashers to pump the detergent from a big drum into the mashine. Thats a good Idea.