dry rock leaching po4 in saltwater not in ro/di water

[vincent1972]

hi,
i have old dry live rock that i put a few weeks ago in a tub with ro/di water.
i had the rock soaked in acid , then rinsed it of .
after that i have put it a tub with fresh ro/di water en treated it with LC.
after a week of dosing LC i stopted the dosing for over 5 days and tested the po4 , there was no po4 left .
so then i mixed ro/di with my salt , tested the saltwater for po4 , there was no po4 in the salt water.
i putted the rock in the tub with the saltwater, with a heater , 2 powerheads and a skimmer to start the curing/seeding of the rocks.

but since the rock sits in the saltwater the po4 level goes crazy.
every day i dose again LC, 2 times a day and after each dose the water turns white , i dose it in a filtersock, but i see a white cloud that goes from the sock into the water .


how is this possible? no po4 in ro/di water but once the rock sits in the saltwater there is po4


thx

vincent

[oseymour]

What type of test kits are you using? Are you using different test kits for fresh and saltwater? Some tests can only be used for saltwater and others for freshwater.

[vincent1972]

the st i'm using is for fresh and saltwater , it can both be tested with the test and i have also a d&d po4 test for saltwater.

but the LC clouds white in saltwater so i have po4.
in the fresh ro/di water it didn't anymore for more than 5 days and after the last dose in ro/di i waited for more than 5 days to test it again and there was no po4 no more

[vincent1972]

nobody?

[bertoni]

I've been thinking about the situation. I don't understand yet what happened.

[machodik]

Hope somebody reply with the comments , I am also anticipating for more ideas on this subject too!

[bertoni]

I'll spend a bit more time on this in a bit, but no promises.

[NEWB2004]

Hey Vincent, I'm not near as sharp as theses folks on this site but I do know what has happened to me. I started a reef tank up around 1999 and inured rock from a friend of a friend and got a great deal... free. I didn't cure it as we weren't doing a lot of that back then. I simply started the tank. I fought outrageous phosphates despite never using anything other then rodi water and no additives other then shrimp and flakes. I did water changes every week for just short of 2 years along with running a phosphate remover almost non stop until it finally subsided. I found out the guy was using tap water with a very high phosphate level..... just my horror stories. My most recent tank I let the rock dry out all summer and then cured in trash can with salt water at 80 degrees with the lid on. Changed cure water monthly. No detectable phosphates in tank for the first 6 mos. Good luck

[vincent1972]

i find it very strange why the rock stopped leaching for over 5 days in ro/di water.
and starts again in saltwater.

[bertoni]

So do I. Maybe some surfaces were not exposed to much flow during the initial curing. That's about all I can think of.

[vincent1972]

the acid soak process i did was for more than an hour

[dkeller_nc]

The interpretation of "no leaching in RODI, but high leaching in saltwater" may, or may not be, correct. It's not necessarily true that a white precipitate when a LaCl solution is added means that phosphate is present. There are several other possibilities for lanthanum compound precipitates, but that'd be a long post with a lot of chemistry geek-speak. The bottom line is that a molybedenum blue phosphate test (like the Hanna Checker) is necessary to assess the phosphate levels in the water.

[vincent1972]

with e hanna tester (i have it also) the po4 in the saltwater is 0.25

[OCReeferr]

Did you have any flow in the rodi water? If I not it sounds like that could be the problem. The water you tested had no phosphate but the water immediately around the rock did. How long have you had it in the salt water with the powerheads?

[Dan_P]

Calcium phosphate is very insoluble. For example, your teeth typically do not dissolve over your life time. Storing aragonite in RO water is to dissolve calcium phosphate is not an effective treatment.

Acid will dissolve aragonite and calcium phosphate, but it takes time. Depending on how deep thick the layer containing calcium phosphate is, how accessible the phosphate layer is to the acid, and how concentrated the acid, a one hour treatment might not be enough. To do this right, you would need to circulate dilute acid and periodically measure the acid solution for phosphate. When the concentration increase stops, you're done. You would have to neutralize the acid solution before testing which is easy if you have a pH meter.

Why did the phosphate appear when the aragonite was placed in salt water? Here's what I am thinking happened. Normally, calcium phosphate is very insoluble, but in the presence of ions like magnesium, the solubility constant for calcium phosphate appears to increase. It doesn't but the concentration of "free" calcium, the species responsible for precipitates, decreases because it forms soluble complexes or salts with magnesium. This is why calcium concentrations in sea water can be higher than the solublity constant of calcium carbonate would indicate without precipitating.

[tmz]

the st i'm using is for fresh and saltwater , it can both be tested with the test and i have also a d&d po4 test for saltwater.

but the LC clouds white in saltwater so i have po4.
in the fresh ro/di water it didn't anymore for more than 5 days and after the last dose in ro/di i waited for more than 5 days to test it again and there was no po4 no more

Not necessarily. The lanthanum may be forming lanthanum carbonate precipitant in the salt water.

[tmz]

Take a liter of ro water and add a capful of lanthanum chloride solution. It will stay clear.

The cloudiness after adding lanthanum to the salt water could be from residual phosphate but is likely from lanthanum carbonate.

Take another liter of ro water and add a tsp of baking soda( sodium bicarbonate) stir and let it settle until clear,then add the lanthanum chloride ;lot's of cloudy precipitant will form.

Salt mixes include carbonate for alkalinity. Lanthanum precipitates primarily with phosphate and/or carbonate.

[bertoni]

Calcium phosphate will dissolve to about 20 ppm in water, so it should be reasonable for leaching phosphate at the levels we typically see it. I'm not sure, though, what forms might be most common in live rock, but calcium phosphate should form as part of the calcium carbonate matrix.

[tmz]

The goal of the lanthanum treatment for new rock is to establish equilibrium with water low in phosphate and to stop any leaching of loosely bound PO4 species from the surface of the rock.

Phosphate in the calcium carbonate matrix is sunk, some for millenia and requires dissolving the matrix( ie the rock) to release it ,some of which occurs when fresh water is used; more when acid is used. The sunk PO4 shouldn't leach since it's enveloped in the crystal matrix; it's possible some of the new surfaces resulting from some of the rock dissolving in the fresh water and residue from the earlier acid bath are adding some though. If the pH pH of the salt water is lower than the freshwater,it might also account for some additional leaching.

Test sample pollution from precipitants is also a potential issue.

The major player in clouding is likely the carbonate in the salt water reacting with the lanthanum, IMO.

FWIW, I use salt water at an sg comparable to with new rock ; test the PO4 after a few days to see if it's leaching,. If so ,lantahanum is used until I get a week or so of low PO4 readings without it.