[Rolo]

Hello everyone, first post on this forum! Some of you might know me fromThe Planted Tank which I frequent very often. Ok, now to my problem:

Here is a link to the post I made on The Planted Tank. It will provide all the specifics as I explored and narrowed down the factors. Here I will just summerize the situation.

A friend of mine put a bag of Shultz Profile into the tank, and filled it with tap water. Nothing but these two, and let it sit for a week. He lost the commitment to keep the tank so passed it too me. Now, when I filled the tank with my tap, I discovered a very large phosphate increase; the tap I filled it with has 0.2ppm PO4---, a few hours later the level were 2.4ppm.

I found out that the orginal tap water used in the tank is loaded with tons of PO4--- (he lives in a farmy, rural area). I read the post titled, "Florabase - PO4 test kit interference" and the issue seems quite like mine. Is it really the Fe in the substrate bonding with PO4---? Tom Barr, does your answer to the that post (Florabase...) apply to my situation?

I believe that since the substrate was initially in phosphate loaded water, the iron reacted and "precipitated" ("" because the iron really isn't in solution, but remains in the substrate). Since adding it to water with a much lower conc., the precipitate was allowed to re-dissolve.

 

[plantbrain]

It might, there's certainly a lot of PO4 potentially absorbed in the spaces, adding water would cuase the redox levels to drop, increasing the solubility to go up, potentially releasing the PO4.

You should be able to fill the PO4 sites up or remove them to get a stable level depending on how much is present and the form in the substrate and the redox etc. It can get very complicated chemically butr whatever the deal is, things should even out soon, keep doing large water changes.
PO4 in the substrate is not a bad thing per se................
If your source tap is low, thaty should cause the substrate PO4 loss, you'll need to add PO4 at some point in the future likely.

Regards,
Tom Barr

 

[Rolo]

It might, there's certainly a lot of PO4 potentially absorbed in the spaces, adding water would cuase the redox levels to drop, increasing the solubility to go up, potentially releasing the PO4.

You should be able to fill the PO4 sites up or remove them to get a stable level depending on how much is present and the form in the substrate and the redox etc. It can get very complicated chemically butr whatever the deal is, things should even out soon, keep doing large water changes.
PO4 in the substrate is not a bad thing per se................
If your source tap is low, thaty should cause the substrate PO4 loss, you'll need to add PO4 at some point in the future likely.

Regards,
Tom Barr

Thanks, this is pretty much what I believed was happening.

However, what did you mean by "absorbed into the spaces" Fe bonding? Simply adsorbed phophate ions, as carbon does? I don't think it has anything to do with CEC since that pertains to cations... I think the answer could be in the same way Phos-Remover removes phophates, since both that and Profile are both similar materials, ceramics.

There really must be a ton of phosphate within the substrate since multiple large water changes never decreased the concentration below 2.4ppm. Surprisingly, no algea outbreaks and the plants are growing well. It is true that PO4--- is better used in the substrate then in the water column correct?

 

[Error]

Hmm

Do water changes of varying amounts affect redox to different degrees? I imagine a small amount of fresh water would change the redox only a little. If this is indeed the case, would a more viable solution to removing the PO4 from the water column and keeping it locked in the substrate be very small, daily water changes for a while? Just a thought; that is if the redox is indeed decreasing enough to leach PO4 from the substrate into the column in the first place.

I suspected a bad test kit at first, but I admit I didn't bother reading the other thread where that issue was most likely already addressed.

A way to test this might be to do water changes of varying degrees for a while and test each time. If you get different results, then bingo.

 

[plantbrain]

No, I see nothing that says PO4 is better than in thwe water column nor see anything to suggest that it's true either in our tanks, quite the opposite.

It can bind to the CEC sites, but...............CEC is for what types of ions? Cations...........what is PO4? An anion.
Doh. Fe sites are well oxidized in the proofile but inside the poroes, there might be many sites that are not oxidized and slightly reduced and therefore able to bind with PO4.

But you have something else going on, liek bad test kit. The substrate will only hold so much and redilution of 2ppm into the water column after a few big water changes points to a bad, kit, not the substrate.

Regards,
Tom Barr