Yup they're nitrate factories.

[HuduVudu]

Since this phrase has been stretched beyond all recognition, I figure I will just completely misuse it.

Plenums, DSBs and I would venture to guess all anaerobic decompostion schemes are indeed nitrate factories. The boxes of nitrate go in to the factory and the finished good is boxes of alkalinity with free nitrogen as the gas coming from the smokes stacks. Some factories are more effecient than others, but it seems that they all produce the same output. I have yet to see in very long term nitrate factories the dreaded nutrient dump, and I have had my nitrate factories up for years. I have found that hydrogen sulfide isn't really the enemy, the real enemy is rapid aerobic nitrification. IME nitrate factories have been very desirable in doing what they are intended to do. Convert nitrate into free nitrogen. With the beneficial (it seems) effect of producing alkalinity.

Today I removed my 8 month old plenums ... for good. They and none of their kind will be returning. Perhaps in the future I will find a niche application that provide a solution for but for now, they are dunzo.

What might you ask is the reason for your sudden distaste for this seemingly beneficial at best, nuetral at worst system?

Well it is the alkalinity. I have been struggling with high alkalinity for a while. This seemed awesome when I was dosing differently, but when I added a calcium reactor this became unteneable. I was at first struggling to diagnose my low calcium. This was confusing and no matter what I did I could not get the calcium up. I even considered calcium chloride, but for me that is a last resort. I don't want the imbalance and I don't want the water changes. So I have been grinding on this for quite a while. My alk has crept up from 8.6 dKh to 10.2 dKh in an attempt to get my calcium over 350 ppm. I have lost one of my LPS and I am frustrated because the tank is very mad and I don't know why. So it finally occured to me that maybe the plenums were the problem. I pondered this over the course of several days and it made sense. My wife wanted to keep the plenums alive until I was sure so I figured I would go to the ocean get my water change water and then perserve the plenums in case this wasn't the issue. Whelp it was. In two days from the removal of the plenums the dKh went from 10.2 to 9.6. I expect it to fall further.

Just something interesting that I wanted to share.

 

[sixty_reefer]

That’s a really interesting perspective. Wend you say plenum you referring to the DSB plenum? And not to a under gravel plenum? Just to confirm

 

[ReefGeezer]

Don't get me wrong here. I am not an advocate for DSBs. I think that in addition to NO2, nitrification of NH4+ yields like 4H+ so I can imagine some potential to affect alkalinity & pH. But...Is reduction of a few ppm of NH4+ really enough to noticeably raise either?

 

[Sean Clark]

This is a nice fresh take on the factory concept. I went another denitrification route so I kind of have the opposite issue of declining alk to deal with. I wonder if I could offset this by adding a plenum and adjusting its volume to match the alk consumption of my existing system.

 

[HuduVudu]

That’s a really interesting perspective. Wend you say plenum you referring to the DSB plenum? And not to a under gravel plenum? Just to confirm

Hmmmm some explaination is in order. These are PVC tubes with a 2" plenum, 2" inert sand and 2" calcium carbonate rubble.

This is after I pulled it and it is in a 5 gallon bucket. Normally this is in my sump or main display depending.
Since a picture is worth a thousand words. Here is picture:

 

[HuduVudu]

Don't get me wrong here. I am not an advocate for DSBs. I think that in addition to NO2, nitrification of NH4+ yields like 4H+ so I can imagine some potential to affect alkalinity & pH. But...Is reduction of a few ppm of NH4+ really enough to noticeably raise either?

Nitrification takes the NH4/NH3 to NO3. This is done aerobically. Anaerobic denitrification pushes everything backwards to get back N2. The chemistry on the anaerobic side is ugly and there is lots of side chains etc ... but ultimately you get back the alk that was consumed in the aerobic process and produce free nitrogen.

I am not sure why the surge in alk. I would think that it would be a one to one product with the alk that was consumed to get to the nitrate but it seems maybe there is something else at play here. Perhaps there is time lag, or storage factor not sure but my observation is what it is.

 

[HuduVudu]

This is a nice fresh take on the factory concept. I went another denitrification route so I kind of have the opposite issue of declining alk to deal with. I wonder if I could offset this by adding a plenum and adjusting its volume to match the alk consumption of my existing system.

Interesting ... what is your denitrifcation process?

 

[HuduVudu]

@atoll & @Subsea you guys might be interested in this.

 

[Sean Clark]

Interesting ... what is your denitrifcation process?

Sulfur reactor. There is an equation somewhere (I do not know it off hand) to show how x nitrate consumed equates to y alk consumption and z h2s generated. RHF has a thread on it.
Right now I manage this by pushing my effluent through a large chamber of Ca reactor media which consumes the h2s, raises the pH back up, and buffers the alk at the same time.

 

[Sean Clark]

My alk consumption is not fully offset by this method. That is what made me consider a hybrid method using both the sulfur reactor and a plenum to complement each other and add a small amount of additional alk.

 

[HuduVudu]

Sulfur reactor. There is an equation somewhere (I do not know it off hand) to show how x nitrate consumed equates to y alk consumption and z h2s generated. RHF has a thread on it.
Right now I manage this by pushing my effluent through a large chamber of Ca reactor media which consumes the h2s, raises the pH back up, and buffers the alk at the same time.

Interesting seems like the sulfur in the reactor favors H2S production.

EDIT: Post out and tag me if you try this, or put it here and tag. Either way I would be intereted in knowing how this works out.

 

[Randy Holmes-Farley]

Unless nitrate is rising or falling substantially, I don’t think there’s any direct effect of the ordinary nitrogen cycle on alk.

If you are now letting nitrate accumulate, alk will decline slowly. If you do not let it accumulate, I cannot see a way to maintain it with any different alk effect than the plenum had, except a sulfur denitrator which greatly depletes alk, or water changes that will slowly deplete alk.

Maybe the alk boost you saw was from CaCO3 in the plenum dissolving due to lower pH in it.

 

[Randy Holmes-Farley]

Interesting seems like the sulfur in the reactor favors H2S production.

EDIT: Post out and tag me if you try this, or put it here and tag. Either way I would be intereted in knowing how this works out.

They generally produce sulfate unless they aren’t controlled properly.

 

[HuduVudu]

They generally produce sulfate unless they aren’t controlled properly.

Does this raise the sulfur in the tank? i.e. does it add sulfur?

 

[Randy Holmes-Farley]

Does this raise the sulfur in the tank? i.e. does it add sulfur?

It adds sulfate, but sulfate is already very high. Third most abundant ion in seawater by weight, so the percentage effect is low.