canister advice

Hi All: I currently have a 404 fluval canister running in my set up. I have removed all but one sponge, all ceramic rings and now only have carbon and phosguard and the sponge in there (the reason I did this is because I'm converting from a FO to a reef and am attempting to reduce my nitrates). I do not have a fuge or sump. Question - should I add some live rock rubble into the baskets? Would this help at all or wouldn't that become basically the same as the principle behind the ceramic rings?
Advice welcome! I'm still battling nitrates.

 

LR would be the same as ceramic rings but rings are going to need to be cleaned.

 

To get nitrate reduction you need low O2 and you need denitrification to occur in the same general vicinity as nitrification. When you use the ceramic rings, or LR rubble, you'll get a biofilm on the surface, and in this film, you'll get nitrification. It is possible that lower down in the film, you'll get lower O2 areas, as the nitrifying bacteria on the surface consumes the 02. It has been shown that you don't actually need a very thick film to get low levels of 02, in the lower layers, where denitrifying bacteria would reside. However, generally most don't think there is much if any denitrification happening on such substrate.

So, assuming this is true, what happens is now the nitrate has to travel a long distance to get to the lower O2 areas, such as the sand and big chunks of LR (the ones with deeper pores), where denitrifying bacteria is more likely to occur. When this happens, the nitrate is dispersed, all over the tank and less likely to come into contact with this bacteria.

However, if denitrification occurred in close proximity to nitrification, the nitrate would be condensed to a smaller area and there would be a more reliable flow to the denitrifying bacteria, as it doesn't travel far and doesn't disperse before reaching the bacteria. So, the population of denitrifying bacteria would tend to be higher and the system would operate more efficiently as the nitrate is now in the right place to begin with. It is believed that if you use large chunks of LR, or sand, as opposed to such ceramic media, or small pieces of LR, this situation described is more likely to occur, as the large LR provides suitable habitats for nitrifying and denitrifying bacteria, in close proximity.

So, logically, such ceramic media could act to increase nitrate rather than decrease nitrate. It does not really provide any other benefit in a reef and may also act to trap detritus, also leading to increases in nitrate. So, generally the consensus among knowledge reefers is to ditch it entirely. Large pieces of LR are generally more than sufficient and more effective for the reasons described.

 

Do you have live rock in the display tank yet? If so...how much?

 

Yes, it's hard for me to say how much it weighs but quite a bit, it's a 54 gallon tank.....I actually removed some a while back so I could create enough room between the rock for adequate flow.....

 

Thank you for the explanation m2434 although I'm not sure I have the smarts to totally understand it

 

D'oh, your over-thinking it then... This is a bit oversimplified, but sufficient for our purposes. The nitrogen cycle goes sort of like this. Fish waste -> ammonia -> nitrite -> nitrate -> nitrogen gas.

The ceramic media supports "Fish waste -> ammonia -> nitrite -> nitrate", but probably not so much the last step "nitrate -> nitrogen gas."

So, then, the nitrate has to travel further to get to bacteria that can complete the cycle. If the nitrate has to travel further to get to the bacteria, it will tend to disperse all throughout the tank and a lot of it can accumulate in areas away from the bacteria. So, nitrate can accumulate throughout the tank, rather than be converted to nitrogen gas. So, the media, in some cases (not always, it depends on a lot of factors), may actually increase nitrate levels.

 

I understand better with the second explanation ....well, I guess somehow I have a lot of nitrate within my tank since I can not seem to export it through various methods. I am currently using biopellets as a method to export but it seems to be taking a much longer period to begin to work than what I anticipated. I guess I've not found a method to create the right environment to accomplish that last step - converting nitrate to gas.....

 

Enough rock in the tank should allow you to eliminate the ceramic media and any additional rock in the canister. How much livestock is currently in the tank and what and how often do you feed the livestock?
Also, is the canister filter the only filtration system on the tank? If so, you should definitely consider a hang-on protein skimmer since you do not have a sump.

 

AS to the canister, I would remove the sponge and ceramic media. These may be helping to increase nitrate (they certainly aren't helping anyways). You could also try removing the phosgaurd.

Also, your Biopellets probably aren't doing much of anything, as you do not have a skimmer. The bacteria on the pellets will reduce nitrate, but then as they slosh off, the bacteria goes back to your tank. If the bacteria can't get enough organics to survive, it would just die and most of the nutrients would go back to your tank. Some may be removed by GAC in your canister, but without a skimmer, you would need a lot and would need to change it often (probably weekly). However, I am not convinced that GAC can replace a skimmer when BP are being used.