Increasing Nitrates by increasing GFO?

[IPWitan]

I guess I am trying to better understand two key points

1 - how one can have bubble algae with 0 phosphates and 0 nitrates (tested at consumer grade equipment) and
2 - why corals "stave" or "bleach" when GFO is used (at zero phosphates)

If you want to increase nitrates in a ULN tank, why can't you increase GFO? Why wouldn't this lead to an increase in nitrates?

No one has recommended this...so it probably doesn't work, but I don't understand why it doesn't work. Any thoughts?

Here is my thought. If macros consume phosphate + nitrates + light to grown, and they will grow to the limit of the least common resource, then if you remove a resource, the the reaction will likewise be limited. Next, plants consume both nitrates and phosphates, but GFO only consumes phosphates. So if you increase GFO (which decreases phosphates), then the available phosphates for uptake by macros should be very low. As a result, if there is no phosphate, the macros cannot consume them along with the nitrates, and the nitrate level would rise.

Notwithstanding, there is a large amount of anecdotal evidence about GFO and starving corals and eventual bleaching, presumably with a lack of nitrates, not phosphates. I don't understand why that would happen using just GFO.

One thought is that nitrates are actively neutralized by live rock and/or the sand bed via the nitrogen cycle. Sand doesn't need to be deep at 4-6 inches, just undisturbed. For example, small portions of the sand bed could act like a DSB and be very effective. Similarly, inside rocks could also house a nitrogen cycle reaction. Thus, if you have a lot of rock, then nitrates will never be high. But as noted this process does not consume phosphates, yet plants still grow. My theory is that plants readily consume phosphates and ammonia before it breaks down to nitrate. Ok, but if you then chemically take up phosphates, then macros starve, the ammonia continues to nitrate/nitrate as usual. But instead of being consumed by macros, the nitrogen cycle consumption increases its uptake and nitrates still go to zero.

It is my understanding that granulated carbon would have no effect on this, but I could be wrong.

Another theory, of course, is that GFO absorbs more than phosphates and whatever it absorbs is required by corals to grow. I know that some research has been on the need for potassium and photosynthesis, but I don't think anything conclusive has been published as it may related to corals.

What is going on here?

 

[Andy V]

I'll get you started, but someone will have to pick up where I leave off...

1. Your algae is consuming the phosphate so quickly that there is very little left in the water column for your test to pick up. It's quite simple...no phosphate equals no algae. Actually no phosphate on earth would pretty much mean no life on earth. So trust your eyes and not the test. If you have algae, you have phosphates, which is good because...
2. See #1 - corals DO need phosphate in order to live. What is zooxanthellae? ALGAE.

As for the rest, there are other bacteria present in the tank that consume nitrates. The answer probably has hundreds of variables, most of which are not understood. But I am sure someone will probably give you a very authoritative, simple answer hahaha.

It's a shame that when you try to do research on these topics that the first several pages of Google are nothing but a bunch of hobbyists repeating the same garbage they hear from other people, instead of actual scientific research.

 

[JohnK]

IIRC the traditional, not necessarily fully scientifically grounded thinking would be, with the whole redfield ratio thing..... and carbon dosing.... Non specific bacterial growth.... nitrate is usually the limiting factor and phosphate more plentiful. If that's correct, then you might have to run a heck of a lot of GFO before you ever tip the scales and make phosphate the limiting factor. If phosphate was the limiting factor, then in theory you could increase GFO to starve out the phosphate and then let nitrate rise a bit. On the other hand, I have heard of people dosing nitrate in an effort to bring phosphate down

 

[IPWitan]

Wondering if a bubble algae bloom could be the cause of all the zero readings. Tested my po4 and no3 and ZEROs across the board. Bubble algae seems happy!

On an unrelated (or maybe it is related) my salinity was likely at 1.021 for an extended period of time. Don't know how that changes things. The refractometer was out of calibration.

 

[wpeterson]

Bubble algae is one of the more hardy nuisance algaes and seems to metabolize despite lower nutrient levels, though at a diminished rate. Also, because of it's structure vs. leafier green macroalgae, it can cluster on live rock which may be slowly leeching nutrients into your tank, putting it higher up the funnel from your chemical/nutrient export in the sump and also preventing source nutrients from reading on your tests (as they're absorbed before being present at high enough levels to measure in the broader water column.

That being said, what John said about the Redfield ratio is also true - offsetting the balance of available nutrients may cause excess of nitrate/phosphate because most algae, coral, and other photosynthetic organisms are consuming them at the 16:1 Nitratehosphate ratios.

If you're managing your nutrient export enough that the only pest with a foothold is bubble algae, you may want to ease up on your ULNS levels before you starve/discolor your corals and focus on targeted management of the bubble algae, emerald crabs are usually the best method.

There seems to be some loose/anecdotal evidence that not all macroalgaes obey the Redfield ratio strictly or have slightly different metabolic pathways for organic vs. inorganic nutrient sources, which is why you may find one last nuisance algae or cyano with a foothold despite low nutrient levels.

 

[G.T]

Nice Read