Rock absorbing nutrients?

[Dan_P]

Okay, I think I understand, but maybe we had different goals.

Let's say you have a running tank without substrate and a known PO4 level. And you wanted to fill that tank with x kilograms of your substrate. Would you be able to predict the PO4 adsorption/binding based on that? Or, could you create a phosphate solution to soak the substrate in, so it would have a minimal effect on the PO4 levels of the tank?

That was my initial goal, but it turned out to be difficult to approximate especially when testing in very small Jars.
In the end, I didn't go the fancy "math/chemistry" way and instead opted for the "engineering" way by simply adding substrate in batches and countering the measured delta in phosphate levels each day by dosing It gets the job done, but is less elegant

I still dropped to undetectable levels a few times (and still occasionally do when adding more)... Some dinos appeared but dosing nutrients and getting all trace elements back into order according to an ICP-MS test fixed the issue quite fast... Oddly enough Strontium appeared to make the difference for the dinos in the end, but I think that was pure coincidence

Have you published any of those studies here on R2R yet? Would be an interesting read

Have not published details yet. Experiment still in progresss.

The small jar approach could have worked or you could have performed the batch treatment with PO4 outside the aquarium before adding it. That would have been done at a larger scale and with ample to test. Stirring the water would have required a small powerhead.

The appearance of dinoflagellates on newly added sand would not be surprising. Dinoflagellate growth on old surfaces after adding new sand would be interesting.

 

[Dan_P]

I think an iterative dose and measure approach would work best. It takes a lot, but one could also substantially overshoot and then be stuck over target.


It can keep on absorbing more and more if the amount in the water is sufficient. Then it could release that later when you try to keep it lower.

Agree ^^^ The maximum concentration can be at or slightly above the target.

A large volume of water to rock volume will ease the pain of frequently dosing phosphate. Observing whether there is progress in saturating the aragonite surface, sand or rock, can be done by measuring the phosphate concentration several times the first day to obtain a baseline adsorption rate. After a two or three phosphate doses, measure the rate again. You don’t need many points. Every six hours can be informative.

 

[EnterName]

Have not published details yet. Experiment still in progresss.

I will be patiently waiting

The small jar approach could have worked or you could have performed the batch treatment with PO4 outside the aquarium before adding it. That would have been done at a larger scale and with ample to test. Stirring the water would have required a small powerhead.

Yes, I just got tired of having buckets full of sand sitting around with nowhere to put them, so I decided to just go for it and hoped small batches wouldn't make a difference in a 171gal tank. Apparently I was wrong, but then again: I run my tank below 0.05ppm PO₄ so the buffer will be limited.

The appearance of dinoflagellates on newly added sand would not be surprising. Dinoflagellate growth on old surfaces after adding new sand would be interesting.

Interestingly the dinos (Ostreopsis spp.) appeared on the little bit of old sand from the previous system that I transferred to keep a little bit of the microfauna (not more than 250mL of sand). And obviously the glass of the new tank was covered as well. The rocks were only slightly affected (that was the point where I actually got nervous).

The dinos pretty much fully disappeared after bringing nutrients and trace elements back to normal. I only see a few Amphidinium spp. cells in some weird inactive state on the backwall (Second image, page 1, post #3 on my thread, they are basically circular instead of oval). The only active cells I see are present on some coral tissue that got hurt during the transfer.

It's really weird how my tank went from Prorocentrum spp., through Ostreopsis spp., to Amphidinium spp. over the years while never really struggling with actual outbreaks, and always side by side with a decent amount of diatoms because my silicate levels were always elevated.