Tripod1404
Active member
I have been reading bunch of thread about nitrate, phosphate and alk. I decided to write something up based on how these parameters are related and how they are related to the corals and to the zooxanthellae.
I think through the years it became somewhat of a "common knowledge" that there are two main approaches to a sucsefull coral tank. First it to have "high nitrate, high phosphate and high alk" and the second is to have "low nitrate, low phosphate and low alk".
One important thing to note here is keeping two of these low and one of them high is stressful for corals. When zooxanthellae (zoox) have access to high amounts of, say nitrate but low amounts of phosphate, they starve the coral of phosphate by taking up all the phosphate that enters to the coral cells. This cause coral cells starve and they either expel zooxanthellae, bleach, starve and die, or they die because of phosphate starvation before they can expel the zoox. First option causes STN, second option causes RTN. Keep in mind there are a lot more stuff that can cause STN or RTN, some of which are pathogenic, this is just one of the potential causes.
Same thing happens in reverse direction when nitrate is low and phosphate is high.
And this all connects to alk based on the demand of corals to zooxanthellae, as well as N and P.
If you have high nitrate and phosphate, you should also have high alk. This way corals can built their skeleton faster. When they built skeleton faster, they can use higher amount of N and P, and the carbon provided by zoox to built soft tissue faster. Newly made corals cells also get some of the zoox as well, so coral cells do not get over run by zooxs.
If you have high nitrate and phosphate but low alk. Rate at which corals grow gets limited by alk. This causes a surplus of N, P and the carbon fixed by zoox simply because corals do not have enough new skeleton to use these for building more soft tissue. All this surpass N and P fuel zoox and causes the intercellular zoox numbers to increase and coral browns. Corals can live browned, but in extreme cases corals will bleach because number of intercellular zoox gets to high that they start to starve the coral cells. So they expel zoox and bleach. This is the case of "my acros were brown but they started to bleach"
If you have low nitrate and/or phosphate but high alk. High alk inevitably cause corals to built skeletons faster but this time corals do not have enough N and P to built soft tissue. As a result, coral cell and the intercellular zoox need to compete for the same limited amount of N and P. This means one of the two would eventually starve. If coral cells starve, they expell zoox and bleach. This most easily happens at the tips (or places that get the most light) since those are the parts of the coral that is growing the most, and so has the highest demand for N and P. That is why increasing alk too fast causes burned tips, it is simply this event happening locally. In extreme cases a coral can completely burn, or in other words, bleach. On the other hand, If zoox starve, corals get pale as they are forced to live with a very low number of zoox. N and P cannot simply support more zoox. If you do this moderately, you get a zeovit tank. In such a tank, there is so little zoox in corals that you simply see the fluorescent proteins of coral against their white skeletons, this is what that makes them very brightly colored. I believe they also produce more fluorescent proteins to protect what little number of zoox they have.
SPS corals are particularly sensitive to N, P and alk because amount of soft tissue they can have is limited by amount of skeleton. LPS can, to some extend, have more soft tissue with same amount of skeleton. A hammer for instance, can have a bigger polyp with more tentacles while keeping the its corallite about the same size. Softies dont even need skeleton, so they are far less sensetive to interplay of alk N and P.
Long story sort, in either case, you should not limit the growth of corals. If one of the N, P or alk become limiting (keep in mind if one is excess it means other became limited), it causes coral and zoox to start competing for the limitted resources. When this happens, there is no point of having a symbiotic relationship. If zoox competing with the coral cells for resources, it is no longer a symbiont but a parasite. This results in coral cells to expel zoox and bleach.
I think through the years it became somewhat of a "common knowledge" that there are two main approaches to a sucsefull coral tank. First it to have "high nitrate, high phosphate and high alk" and the second is to have "low nitrate, low phosphate and low alk".
One important thing to note here is keeping two of these low and one of them high is stressful for corals. When zooxanthellae (zoox) have access to high amounts of, say nitrate but low amounts of phosphate, they starve the coral of phosphate by taking up all the phosphate that enters to the coral cells. This cause coral cells starve and they either expel zooxanthellae, bleach, starve and die, or they die because of phosphate starvation before they can expel the zoox. First option causes STN, second option causes RTN. Keep in mind there are a lot more stuff that can cause STN or RTN, some of which are pathogenic, this is just one of the potential causes.
Same thing happens in reverse direction when nitrate is low and phosphate is high.
And this all connects to alk based on the demand of corals to zooxanthellae, as well as N and P.
If you have high nitrate and phosphate, you should also have high alk. This way corals can built their skeleton faster. When they built skeleton faster, they can use higher amount of N and P, and the carbon provided by zoox to built soft tissue faster. Newly made corals cells also get some of the zoox as well, so coral cells do not get over run by zooxs.
If you have high nitrate and phosphate but low alk. Rate at which corals grow gets limited by alk. This causes a surplus of N, P and the carbon fixed by zoox simply because corals do not have enough new skeleton to use these for building more soft tissue. All this surpass N and P fuel zoox and causes the intercellular zoox numbers to increase and coral browns. Corals can live browned, but in extreme cases corals will bleach because number of intercellular zoox gets to high that they start to starve the coral cells. So they expel zoox and bleach. This is the case of "my acros were brown but they started to bleach"
If you have low nitrate and/or phosphate but high alk. High alk inevitably cause corals to built skeletons faster but this time corals do not have enough N and P to built soft tissue. As a result, coral cell and the intercellular zoox need to compete for the same limited amount of N and P. This means one of the two would eventually starve. If coral cells starve, they expell zoox and bleach. This most easily happens at the tips (or places that get the most light) since those are the parts of the coral that is growing the most, and so has the highest demand for N and P. That is why increasing alk too fast causes burned tips, it is simply this event happening locally. In extreme cases a coral can completely burn, or in other words, bleach. On the other hand, If zoox starve, corals get pale as they are forced to live with a very low number of zoox. N and P cannot simply support more zoox. If you do this moderately, you get a zeovit tank. In such a tank, there is so little zoox in corals that you simply see the fluorescent proteins of coral against their white skeletons, this is what that makes them very brightly colored. I believe they also produce more fluorescent proteins to protect what little number of zoox they have.
SPS corals are particularly sensitive to N, P and alk because amount of soft tissue they can have is limited by amount of skeleton. LPS can, to some extend, have more soft tissue with same amount of skeleton. A hammer for instance, can have a bigger polyp with more tentacles while keeping the its corallite about the same size. Softies dont even need skeleton, so they are far less sensetive to interplay of alk N and P.
Long story sort, in either case, you should not limit the growth of corals. If one of the N, P or alk become limiting (keep in mind if one is excess it means other became limited), it causes coral and zoox to start competing for the limitted resources. When this happens, there is no point of having a symbiotic relationship. If zoox competing with the coral cells for resources, it is no longer a symbiont but a parasite. This results in coral cells to expel zoox and bleach.
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