Leaching phosphates from rock

[425nm]

So my question is what form of phosphate are most aquarium test kits actually testing for and how useful is that information?

If anyone has a link to what titration/chemical reactions various companies use that would be great.

[asylumdown]

Alright I'm home! Realized last night that I turned my skimmer off right before I left and forgot to turn it on. 2 weeks with no skimmer. Oops. My rocks are looking a little slimy.

Originally Posted by syncro

I'm interested!

I have wondered if phosphates were leaching from my sand or rock. To test, I left sand, rock and nothing (control) in small containers with DI water for a week. Measured 0 phosphates with a seachem test kit. But still have cyano. Dosing nitrates seems to help green algae outcompete cyano where nitrates are always 0 (it also helps bacterial blooms!).

Well to put it one way, what you think of as 'cyano' is actually significantly more complex than that. Much like a forest looks like a homogenous blob of green from space, 'cyano' sheets that carpet your sand and rock work in your tank are actually complex assemblages of organisms that have the emergent property of looking like a slimy, homogenous red/brown. However, those microbial mats are in fact "...compressed laminated microbial communities composed of diverse photosynthetic procaryotes (oxygenic cyanobacteria, anoxygenic photosynthetic bacteria), eucaryotic microalgae (diatoms, chlorophytes, dinoflagellates), and both heterotrophic and chemoautotrophic bacteria" (Stahl et al., 1985 quoted from Pearl et al, 1993). The specific assemblage will be determined by the environment, the conditions, and I believe some stochastic randomness of what happens to be present in that particular location. The organisms making up the mat stratify themselves within the assemblage according to micro gradients of oxygen and light availability, and through what can only be described as an ecosystem feedback effect "cooperate" (more like self sustaining negative feedback loops than true cooperation) metabolically to produce highly resilient communities.

"cyano" mats are often associated with some of the most oligotrophic (i.e., nutrient poor to the point of being hostile to life) water on the planet, often being the sole to primary agent of biological productivity in those habitats. There is strong evidence to suggest that at least some organisms that make up mats of cyano can actually fix dissolved atmospheric nitrogen directly from the water column, which gives cyanobacteria a serious competitive advantage in nitrogen poor waters. They're also incredibly effective at sharing resources. That is to say that within a cyano mat, the waste product of one organism is effectively the food for another, creating an incredibly efficient carbon and nitrogen storing ecosystem. Once a nutrient is captured by the mat, it can effectively be recycled indefinitely (i.e., there's little to no loss of organic C or N from the mat). Because cyano mats are not just plain plants (photoautotrophs), but also contain heterotrophs and potentially even photoheterotophs (organisms that capture dissolved organic carbon from the and use light for energy), they're incredibly efficient at scavenging dissolved organic matter from the water column as well.

So, and this is only conjecture obviously, what I think is happening when people add biopellets (or any other carbon source) to their tank, especially at a late stage in the game when there's likely already small patches of these cyano assemblages present, is that they have effectively dumped a massive amount of dissolved organic carbon that microbial cyano mats are specifically evolved to efficiently scavenge at the same time that available nitrogen levels plummet, giving nitrogen fixing cyano mats an even stronger competitive advantage. Once the mat is established, it's extremely difficult to get rid of it because of the efficient way in which the mat hangs on to what it accumulates, you can reduce your nutrients until all your corals die, and the cyano, once established, will likely be able to persist. I think the key to good results with any kind of carbon dosing system is doing it in such a way that gives advantage to the species of heterotrophs that you do want, so that there's not a massive excess of dissolved organic carbon floating around in the water column for cyano to capitalize on. Whether this means setting up your carbon dosing system from day one so that the heterotrophs you do want are already consuming all the carbon before the species that make up make up mats of cyano are introduced or some other method I don't know about, it makes sense to me that cyano will always be a risk with any sort of carbon dosing system.

Originally Posted by 425nm

So my question is what form of phosphate are most aquarium test kits actually testing for and how useful is that information?

If anyone has a link to what titration/chemical reactions various companies use that would be great.

And I think the test kits we use are testing directly for reactive phosphorous, aka phosphate (PO4^3-) AKA orthophosphate. The only method I know of that uses only one reagent is the molybdovanadate, which is what I *think* is in the Hanna checker powder pillows. There's also an ascorbic acid method, but I'm pretty sure it uses two reagents, but I'm not 100% sure. I'd have to look at my manuals again, I'm going off what I can find on the Hach website as Hanna irritatingly doesn't publish their reagents. Testing for total phosphorous in a water sample involves doing a more serious acid digestion, so I doubt there's any test kit a hobbyist could by that would do that.