Change of filter media to all foam has affected nitrates unexpectedly !!!

[hamfistUK]

Roughly 5 months ago I changed all the filter media in my 3 x canister filters on my 130g tank to all foam. Previously having had a bit of foam but mainly Seachem matrix and other ceramic media in them. THis tank had not been having any problems but I had been convinced that all foam was at least as good if not better than specialist media. Anyway, the tank has continued to very effectively clear all ammonia and nitrite - no problems. Just FYI, the tank has no real plants.
The tank had previously run at a very steady 20-30 ppm nitrates. My tank maintenance and water change schedule has not changed. The fish load and feeding is pretty much the same. However ........ and here's the punchline ....... now with the all foam media the tank is running at <5 ppm nitrates. Whats going on ? Its great, but I don't understand how this can happen unless somehow I have created anaerobic areas within the foam which has become a nitrate reactor. I am certain that nothing else has changed in the tank except the change of filter media. Has anyone else experienced anything like this ?

 

[Ichthys]

Have the nitrates in the tapwater changed?

 

[hamfistUK]

Have the nitrates in the tapwater changed?

No, its remineralised RO, zero nitrates going in. Excellent question though !

 

[Ichthys]

Ok so it seems like you have dentrification. In theory it's possible whenever the flow through a filter gets all its oxygen removed. But that would take a lot of foam and an extremely slow flow rate, and it would need to be constantly slow. In my attempts to make diy nitrate filters it was difficult to keep the flow slow enough. The slightest increase and it just trickles nitrite back into the tank because the job is only getting half done.

I think it's more likely that it's the test kit behaving differently for some reason? If it's a liquid kit you have to be very violent with the reagent #2 bottle. Shaking is NOT enough, and over time one of the ingredients will totally precipitate out, leading to strangely low readings.

Give it a good thrashing, if you don't already, and/or try a new test kit?

 

[hamfistUK]

Ok so it seems like you have dentrification. In theory it's possible whenever the flow through a filter gets all its oxygen removed. But that would take a lot of foam and an extremely slow flow rate, and it would need to be constantly slow. In my attempts to make diy nitrate filters it was difficult to keep the flow slow enough. The slightest increase and it just trickles nitrite back into the tank because the job is only getting half done.

I think it's more likely that it's the test kit behaving differently for some reason? If it's a liquid kit you have to be very violent with the reagent #2 bottle. Shaking is NOT enough, and over time one of the ingredients will totally precipitate out, leading to strangely low readings.

Give it a good thrashing, if you don't already, and/or try a new test kit?

Another good thought but I use the same (Sera) nitrate kit on other tanks and those are reading their normal expected readings, so I am confident the test kit is OK.

I am pleased, but completely stumped as to what's going on.

 

[Ichthys]

You don't have some kind of "denitrifying sponge" in there by any chance?

 

[hamfistUK]

You don't have some kind of "denitrifying sponge" in there by any chance?

Nope, just standard Eheim sponge discs.

 

[MaloK]

Nobody knows why it happens sometimes. But you are not alone reporting this, Your experience aligns with some other Aquarist have also observed.

 

[sharkweek178]

I think it's more likely that it's the test kit behaving differently for some reason? If it's a liquid kit you have to be very violent with the reagent #2 bottle. Shaking is NOT enough, and over time one of the ingredients will totally precipitate out, leading to strangely low readings.

Give it a good thrashing, if you don't already, and/or try a new test kit?

You have to shake that bottle good and hard 2 for at least 2 minutes. Shake it like it owes you money.
And then after adding the drops from bottle 2, you have to shake the test tube for a minute.

 

[hamfistUK]

You have to shake that bottle good and hard 2 for at least 2 minutes. Shake it like it owes you money.
And then after adding the drops from bottle 2, you have to shake the test tube for a minute.

Read Comment #5. Test kit is a good one.

 

[Fishfunn]

and here's the punchline ....... now with the all foam media the tank is running at <5 ppm nitrates.

I dont understand how your foam is working better than SeaChem Matrix and ceramic stones either. Maybe you are feeding your fish less food or a different brand?

The only way I have been able to keep my nitrates close to 0 ppm is by using chemical filtration in the last stage of my canister filter. I am using Nitra-Zorb and Purigen. They are really working for me; otherwise, trying to keep the nitrate level below 20 ppm with water changes was very time-consuming for larger fish in a large community tank.

 

[MaloK]

Coarse Foam is a surprisingly good biological support. After testing a good load of them I'm back to that.

I been able to maintain 0 nitrates in many tanks with plants, light, and fertilizer alone. But it's not the case here...

Something "Magical" is happening

 

[Fishfunn]

Coarse Foam is a surprisingly good biological support. After testing a good load of them I'm back to that.

I been able to maintain 0 nitrates in many tanks with plants, light, and fertilizer alone. But it's not the case here...

Something "Magical" is happening

Ok, I'll try adding more coarse foam to my filter stages and see what happens.

 

[MaloK]

Ok, I'll try adding more coarse foam to my filter stages and see what happens.

At the moment I'm using a coarse sponge as my intake cover and 2 stages of 3 in my filter is the same one. I add a golf ball size of wool on the top (it's a HOB) and it seem to suffice to provide mechanical filtration requirement...

I force the sponge on the intake to work more as a mechanical filter because I cruelly rinse it under cold tap water until completely clean all the time.

For the last months I only had to maintain this part.

It is assisted by a large air powered sponge filter with a medium grit sponge and an air pump rated for the tank size. It's main purpose is to aerate the water maintain a clean surface and build as much algae as possible directly on the sponge. Water flow is not really relevant there, I wait until they becomes a block of clay before rinsing them.

In the last months, I carefully played with, and giving a chance, replaced nearly all of these medias except my intake cover, and not a single sign of nitrogen showed off.

Keep in mind that the tank itself is filled with plants competing for food...

But the best advice I can give is "The less your biological support clogs" the better. If you can put an easily maintainable mechanical filtration in front and be able to disturb it the less possible. The best.

 

[Fishfunn]

Keep in mind that the tank itself is filled with plants competing for food...

But the best advice I can give is "The less your biological support clogs" the better. If you can put an easily maintainable mechanical filtration in front and be able to disturb it the less possible. The best.

I have a small planted tank with a HOB filter and floating duckweed that always has 0 nitrates. I attribute that to the duck week since it grows so fast and I skim a lot off each week.

The coarse foam at the bottom of the canister is for removing bigger particles that can clog the upper stage of ceramic rings that house beneficial bacteria, but I really think foam as a replacement can house just as much or more bacteria. I'm going to start replacing those with foam.

I do like having the last stage of the canister for chemical filtration. I also believe charcoal can house as much or more bacteria than ceramic. I have a bag of charcoal in the HOB of my smaller tank that I just leave there for that purpose.

I am going to replace some stages in my canister filters with the bio-foam today.