Looking for some assistance with really basic nitrogen cycle question.

[rocknut]

IMO the capability for Live rock to denitrify is very exaggerated among reefers. Yes it will be anaerobic areas deep into narrow canals in the rock but anaerobic conditions is only one of the demands for a good rate of denitrification. The second demand is a fast organic carbon source and the third is the presence of nitrate itself. If – I say if – there is a denitrification of some nitrate deep in the rocks – how will new nitrate be transported in to this area if there is not any water movement through the pores? And if it is such a movement – how do you know that the environment still will be anaerobic. Some has suggested that all of the pores has different animals that’s moving around and their movement will bring new nitrate into the pores – yes – but do we know any animals that are common in anaerobic conditions? I have very difficult to combine anaerobic pores in living rocks with continuous flow of DOC and nitrate – at least in my mind

The same problems will occur in order to explain denitrification as an pathway for nitrogen removal in swallow sand beds and pores in the back side of the grains. Flow of nutrients and still have an anaerobic situation?

Even in normal DSB – there is some problems to fully explain denitrification. it is easier in Jaubert systems and slow normal under gravel filter and reversed under gravel/DSB


No but I not sure that the normal is low phosphates and high nitrates in a system without different types of phosphates removal. Most people use GFO (or similar), cure their living rocks. Take away different organic compounds and so on. All of these things will favor a low level of phosphate. The main pathway for nitrogen into the aquarium (at least in newly started and aquaria without DSB and sediment traps) is not through organic matter – but through the gills of the fish. The surplus nitrogen from fishes is ta 80 – 90 % coming from direct secretion through the gills as ammonia ions (NH4)

However in more mature aquariums – especially aquariums with DSB and sediment traps – the secretion of ammonium ions (NH4) through bacterial breakdown of particle organic matter and from bacteria with capability to use DNRA can be higher. Normally this type of heterotroph bacteria breakdown is limited by fast organic carbons (DOC) – especially for the bacteria in the DNRA group



IMO to add a higher organic load to the system will be a longer way to achieve what you want and new problems will arise during the travel – in some way you can make a parallel with to use Big Bertha instead of a Salong rifle in order to kill a house sparrow

You write in other posts that you have run the aquaria as ULNS before and this can indicate that you have taken away all of the normal phosphorus reserves that you normally have in an aquaria. Reserves that automatically will be transferred to orthophosphate if the system will run low of this important nutrient.


What’s your actual NO3 level?

Sincerely Lasse

Hello Lasse, I did have a ULNS system in the past, but that was before I re-booted this current system. About 18 months ago I broke this tank down, sold all of the live rock and animals, then after a two week wait, bought all new live rock (of much better quality) and started over. I did run GFO for about two weeks about a year ago, just to clean up some phosphates that spiked when the tank was new. The long story here is that my live rock is from an aquacultured source in the Gulf of Mexico, and when ordered, is brought to the surface from the ocean floor, and shipped via airplane, in bags of seawater, so there will be minimal die off. During the first month, there is still a cycle from different organisms that still do die off, so you have to be committed to make some BIG water changes if ammonia ever spikes. After the tank went through its cycle, there was still a large concentration of phosphates (can't remember the exact number, but it was really high, something like 100 ppb). At this point I ran one round of GFO and reduced phosphates down to 0.05 and then removed it, and haven't run any GFO, or other phosphate removers since then.

As of today, I was able to reduce my nitrates down to about 5 or 6 using the Red Sea Pro Test. I have been able to do this via several (I believe six total) 25% water changes, over the past three weeks. I would be totally happy keeping the nitrate at this level, as it seems that many SPS keepers say this is a good number for colors, and overall coral health. However, I am assuming that without any phosphate in the water, this will rise back up until I make another big water change.

I did hook my bottle of NeoPhos to my doser last night, and am dosing 5 ml/day to try to get some detectable phosphates in the water. I will continue to check phosphates and nitrates each night. I am figuring that this will be the balancing act: once phosphates come up a little, nitrates should begin to drop, correct? If/when this happens, would I then cut back on my carbon source, and the NeoPhos so I don't totally bottom out both PO4 & NO3? As you mentioned in your post regarding dosing NoPoX, I am being very conservative, and am only dosing 2ml/day at this point.

Point taken about adding bioload to balance the tank out as opposed to just dosing some phosphorus - that makes sense. At this point I still only have six fish, so would still remain at the low end of bioload for this size system, and will hold off on adding anything else. Also interesting point about the amount of denitrification coming from the live rock. As I mentioned in my earlier post, I would ultimately like to stop dosing a carbon source, and start growing macro algae instead. I am assuming that once my PO4 comes up a little, and NO3 drops a bit, I could then start reducing the carbon source a little at a time, so the system's nutrients can start to level off, and reach some sort of equalibrium? Once I have some balance, I should be able to grow some macro to keep levels in check?

Again, thanks to you, and everyone else for all the advice/help. I know I am very fortunate to have so many knowledgeable people to learn from.

 

[Lasse]

Yes – when you read some phosphorus in the evening – its time to slow down on the phosphorus addition (in first hand) and if your nitrate goes down – slow down the carbon dose and introduce macro algae. That’s a plan that I would follow. One trick you can use in order to control if you have any internal phosphorus production is to measure the level in the morning – before the lights going on and also to analyze for phosphorus just before the lights go of. You probably gets some surprising results – higher in the morning and lower in the evening. If you does not get any reading in the morning – keep on add phosphorus – if you get in the morning but not just after the light goes off – still ad some phosphorus. When you read some just before the lights goes out – stop adding.



Sincerely Lasse