Could A Sponge Filter Increase Nitrate Levels

[Fishmanic]

I have a fully stocked 29 gallon tank.   I recently added a sponge filter to supplement my penguin 200 filter. I feed a small amount of flake once per day and add 1 algae wafer. My stocking is in my signature.    I notice a lot of the detrius (food and fish waste) are attracted to the sponge filter and there is less on the substrate than before installing the filter.  I have a pretty powerful air pump that is attached to the filter.   I have been cleaning the sponge filter weekly  and a lot of fine waste comes out when I squeeze the sponge.
 
  Could the waste in the sponge filter be breaking down quicker as it is in the water flow through the filter.  My nitrates were reading over 40 before I did two water changes.    I did a 50% water change 4 days ago and did a 50% water change today.  I syphon any detrius on the top of the sand.   I will be doing another 50% water change in 2 days.  After the last two water changes the nitrates still read about 40 ppm.    I wondering if I should stop using the sponge filter to possibly lower nitrate levels.

 

[nortonmad213]

whats your nitrate level straight out of the tap?

 

[DrRob]

whats your nitrate level straight out of the tap?

 
Excellent question, could well be the culprit.

Otherwise, if it's made a noticeable increase to the biological filter power then I'd be very keen to leave it alone and let it do it's job.

 

[TwoTankAmin]

Think about what is being asked here for just a minute. Why would nitrate in a tank elevate in relation to cycling. To understand why I am asking this, what we all know.
 
1. Cycling a fw tanks basically enables a tank to convert all the ammonia to nitrate (with nitrite being in between).
2. The ammonia in a tank can only create X amount of nitrate or less.
3. If one is cycling a tank and puts an adequate number of filters on the tank and then cycles using 3 ppm of ammonia, doubling the number of filters will not increase the number of bacteria in a tank at all. The only thing that will do that is greater concentrations of ammonia.
4. There are basically three ways to have nitrate in a tank: 1. It comes in with one's tap water. 2. Cycling the ammonia creates it (so increasing the ammonia would up nitrate). 3. Tank additives create it- most notably plant ferts.
 
If the amount of waste in your tank is relatively constant, and your water change regimen is the same, the the amount of waste created and removed via weekly maint. should not change much either. In fact, adding filtration that traps mechanical wastes, as long as the cleaning is done regularly, should actually help to reduce nitrate some as you should be removing more of this waste than before the sponge went in.
 
Given the above facts, something else besides that new filter is at work. It may be as simple as a the flakeyness of the nitrate kits. Otherwise, look elsewhere for the explanation. as in #4 above.

 

[PrairieSunflower]

I got the impression the OP already sounded as though they had a cycled tank and that the sponge filter has been added on top of that... so I'd think cycling isn't really the issue.
 
I use only sponge filters in my tank and they haven't caused raised nitrates ever, not even in rare times I've had to change the sponges.

 

[eaglesaquarium]

That's true, but the point TTA is making, I believe is that without an increase in bioload, there shouldn't be an increase in nitrates.  The addition of an additional filtration medium shouldn't increase it.
 
 
However, I think that FM's question is related to the fact that the detritus, which used to sit on the surface of the sand, fairly undisturbed is now stuck in the sponge, which allows it to have more flow over it, and I think he's wondering if the poo, etc is breaking down more quickly in the sponge than it was on the surface of the sand, given its new conditions.
 
 
I don't know that it would or wouldn't break down faster sitting in the flow inside the sponge, as opposed to just sitting on the surface of the sand.  For me, the fact that the detritus is sitting in the sponge and not on the surface of the sand would be enough for me to just leave the sponge in the tank as part of the process.  Increasing the frequency of sponge rinses might well have an impact on the nitrate level, assuming that the detritus is breaking down faster in the sponge than elsewhere.
 
 
But, I think its more likely down to the fact that nitrate tests are notoriously erratic.  I don't put a ton of stock in them.

 

[DrRob]

Indeed. I wasn't thinking along the lines of the tank being uncycled, although I was considering the possibility of a bit of anaerobic stuff going on in the substrate that now isn't happening. Hence my comment about the power of the biological filter, which I admit I should have been more detailed on, my question was, was this related to more aerobic biological filtration taking place, which could be related to the mechanical abilities of the filter to provide oxygenated flow, rather than the total surface area for bacterial colonisation? I had also made the assumption that all was totally well before.
 
Oh, and I had also overlooked the obvious answer that the tests are rubbish. Mainly because I don't really worry too much about nitrates, given that I add them to all of my tanks routinely anyway.

 

[TwoTankAmin]

There is not a huge difference in O levels for organic matter in a sponge or on the surface of the substrate. Since most of the organic decomposition in a tank is aerobic, I do not see that there sould be much of a difference in nitrate levels.
 
The one difference I do see would relate to what happens to the organic matter once on the substrate vs in a sponge. Gunk on the gravel will start to break down just like it would in a sponge, with one big difference. On the gravel some of it is likely to work its way deeper and if it gets to where O levels are insufficient, the process greatly slows ultimately becoming an anaerobic process. In a sponge the O is pretty constant and the breakdown would continue as long as the sponge did not get really clogged..
 
However, if one is doing a weekly surface vacuuming vs rinsing out a newly added sponge filter, I cannot see there being a huge difference. The sponge is just collecting some of the gunk as opposed to its laying on the substrate waiting to be vacuumed or to be broken down. At the root of ammonia are two basic causes. The first is fish waste which would include the NH3 exhaled by fish as well as their poop. The other is organic waste from plants or uneaten food etc. being broken down. At the heart of this process are two basic functions- the recycling of carbon and the recycling of nitrogen.
 
However, I will admit my understanding of the details of the decomposition of organic matter is a lot more sketchy than my understanding of cycling related issues.

 

[Fishmanic]

I tested the tap water and it came back as about 10 ppm.   One note---my other tank is a 35 gallon tall hex with an aquaclear filter and no sponge filter at the moment (will be getting one soon) and the nitrate level is at about 20 ppm after it's weekly water change--so it is far less than the 29 gal.  Stocking level is on the high side in the 35 gallon.  

 

[TwoTankAmin]

Any plants in either of the tanks?

 

[Fishmanic]

I have anubias and java fern and moneywort in the 29 gal tank.  I did a third 50% water change in a week and levels are now at 20ppm and my tap is 10ppm so  I should be ok for now.   Will keep an eye on it to see how fast it builds up.

 

[TwoTankAmin]

Those plants should take up some nitrate. My feeling is at the levels of nitrate you are mentioning and the quality of the test kit we have in the hobby suggest that you are probably just fine.
 
It is hard to compare tanks because each one is a bit different. Things like differences in feeding, activity of fish, organic debris, water change differences etc. etc. can all explain why two similar tanks are not.
 
In a tank with 40 ppm of nitrate having a 50% water change with 10 ppm nitrate water means the result should be about 25 ppm. I am not so sure how accurately our kits will pick up on that difference. Shake the bottle differently, have a drop size be a little different, have the water in the test tube be a few % more or less relative to 5 ml, any and all of these things can cause a difference of a few ppms down at the low end.