My memory is terrible, but I am pretty sure that I just used my fresh IO mix for my reef tank, but I did run a large reactor of Al Oxide on it to make sure that all of the po4 was out of the water before I added. I used RO for top off.
FWIW - my IO mix is to 1.026, heated to 78 with enough cacl to get the calcium to 425 and then a few days blowing off co2 after I add enough muriatic to bring the alk down to about 7. This might be important since most salt mixes are incredibly high on some things and I try really hard to bring those down to tank/ocean like levels before I use it. I also use the whole bag of IO so I don't get inconsistent measuring from dry in-container settlement. Salts mixes in general are more reliable if you use the whole container at once - people get lots of different precipitates if they don't. My point is that the precipitate could have come from anywhere, and I try the best that I can to make sure that my salt mix does not have any.
On my end I use Instant Ocean that I use to replace daily skimmate production. As part of my phosphate adsorption studies, I specifically looked for evidence of precipitation when aragonite and IO are mixed. Nothing visual nor chemical (pH, alkalinity, [Ca++], turbidity) detected precipitation.
Just curious, but did you use full strength seawater and heat the water? Both seemed to make a difference, just like Dr RHF said that they would. I also used a powerhead and a reactor. Did you use power this time? I think that it makes a huge difference allowing water to penetrate the pores in whatever media you choose. Remember that microfauna, powerheads. etc. all do move water into rock and sand structures to some degree, although not likely as much as a powerhead would, but time is also a factor with rock and sand in a tank.
I use full strength seawater and mix more strongly than a powerhead. In my experiments, the water can form a whirlpool. Yes, water motion is important, even for coral, because it reduces the thickness of the stagnant boundary layer that exists on all objects in water.
With time, a reactor and power, you can use structure area and not just surface area.
I am going to put some aragonite special grade reef sand in a reactor and see how much po4 I can add before I reach something like .1 or .2. It will be a lot.
On a mg PO4 per gram of sand, how much adsorbs depends on the sand grain size, possibly the mineral type (aragonite, dolomite, calcite, etc.), and the equilibrium phosphate concentration. With good mixing the adsorption only takes 1-4 hours.
It is somewhat confusing to report a ppm reduction in phosphate for a mass of sand or rock because the ppm reduction will be large if the amount of water is small or it will be small when using a large amount of water.
@Garf observed this recently. When I recast his observations to mg/g, fantastic became normal.
I just need to figure out how to measure how much po4 to add - probably made a strong solution and add until my hannah reads .1 in 10g of sample water... then just add increments of that solution to the 10g.
The 2 teaspoon of TSP per 5 gallons ratio works out to be roughly 125 ppm for the dodecahydrate, most of which precipitates as calcium phosphate.
You can make concentrated phosphate solution in RODI and then add a small dose to achieve your desired phosphate concentration in seawater without altering the salinity. I found 6000 ppm PO4 in RODI to form a precipitate where it is added in IO. So, if you make such a high concentration, stir well when dosing. Happy to help if you want.
I have a new reactor and powerhead... and I will clean out a tank with strong muriatic and let that sit for a few days. That is about as sterile as I can get. My hypothesis is that a slightly larger substrate size in a powered reactor will absorb much more than passive. I will create a thread in the experiments section with progress unless it just gets bombarded by idiots and then just record results until I am done and then post the results.
HaHa, I am sure you won’t be bombarded. Besides, your data will confirm that you are right, the adsorption rate will be faster in moving water. Given enough time though, the sand in stagnant water should catch up unless there is a secondary effect like surface fouling in the stagnant water treatment.
I found that aragonite sugar sand with high energy mixing will absorb most or all it’s going to adsorb in a couple hours. Desorption is faster, 15-30 minutes.
This will be an interesting study.
Just a reminder - I am not a scientist. Most of the science that I know is from reefing, reading Dr RHF articles, googling things and articles in TFH and Reef magazines whey they still were printed. It is not nothing and I am not dumb, but I am a novice compared to most. My main goal is pretty much help in actual tanks. My main goal back then was to convince people that dry rock is no bargain if it is loaded in po4, that they should not be adding po4 if they have a trace since it can take SO much effort, media and money to get it back out, etc. My goal now is just to show people that if they have X reading in the tank, then they likely have X * Y bound somewhere... then try and let them know how long before X turns into X*2 or X*4 which might be deadly, or estimate how much they need to lower it. For example, if they read .2 now, with 100kg of rock and sand, then they might have 25 total ppm bound up... and that 75ppm more will raise them to .5 in the tank, which could be deadly for them. With a tank at 10 months, that is 2.5 ppm per month so far, so they have something like 30 more months before potential disaster. Just like the UWC science-type stuff, my focus is on the end-user and hobbyist. This also could be that I lack the equipment and knowledge to do anything more legit.
Good luck! Looking forwards to seeing yourresults. I can never get enough data
