Removing Silicates

[second_decimal]

So I have been in a discussion with a good friend about diatoms, Dino’s and silicates. Lots of info about those things in previous threads but cause of diatoms and Dino’s not really at issue here. The basic question was if DI media dwell time had any effect on DI exhaustion rate. This was prefaced with the understanding that 0 TDS is not an indicator of exhaustion.

It is my understanding that colloidal silica is mechanically filtered and ionic silica, along with any other ionic contaminants, is addressed with DI media. Since that exchange process happens on an atomic or molecular level, It would seem pretty linear for the main method of DI media exhaustion to be volume with a minimum requirement for dwell time at best. I was wondering if anyone had any input on that subject. Thanks.

 

[Dan_P]

So I have been in a discussion with a good friend about diatoms, Dino’s and silicates. Lots of info about those things in previous threads but cause of diatoms and Dino’s not really at issue here. The basic question was if DI media dwell time had any effect on DI exhaustion rate. This was prefaced with the understanding that 0 TDS is not an indicator of exhaustion.

It is my understanding that colloidal silica is mechanically filtered and ionic silica, along with any other ionic contaminants, is addressed with DI media. Since that exchange process happens on an atomic or molecular level, It would seem pretty linear for the main method of DI media exhaustion to be volume with a minimum requirement for dwell time at best. I was wondering if anyone had any input on that subject. Thanks.

Ion exchange occurs pretty quickly. I would say that DI exhaustion rate is solely driven by the total number of ions removed, concentration times volume. Time does not enter into depletion rate.

 

[Randy Holmes-Farley Verified Community Expert]

So I have been in a discussion with a good friend about diatoms, Dino’s and silicates. Lots of info about those things in previous threads but cause of diatoms and Dino’s not really at issue here. The basic question was if DI media dwell time had any effect on DI exhaustion rate. This was prefaced with the understanding that 0 TDS is not an indicator of exhaustion.

It is my understanding that colloidal silica is mechanically filtered and ionic silica, along with any other ionic contaminants, is addressed with DI media. Since that exchange process happens on an atomic or molecular level, It would seem pretty linear for the main method of DI media exhaustion to be volume with a minimum requirement for dwell time at best. I was wondering if anyone had any input on that subject. Thanks.

Before getting into the weeds on silicate and ro/di, why are dinos part of the discussion?

I want to be sure there is no misunderstanding on your friend’s part.

 

[second_decimal]

lol that’s how the discussion started. I recently changed and upgraded my DI after 5-6 months of setup (acid washed and bleached rock). Diatoms / Dinos came and never cleared. So, I was suspicious of my DI that had not shown any signs of depletion at all. It finally popped above 0 TDS and a spent DI system seems like a pretty good fit for unwanted algae growth.

 

[second_decimal]

That’s turned into dwell time (or maybe it started there I don’t remember) and now has evolved into keeping those DI cartridges running efficiently.

Spectrapure, for instance, is claiming a DI resin stage as a “roughing” stage that allows x 3-4 life extension of subsequent DI stages.

Furthermore, it was posed that if you could align (polarize) water molecules through an electrical or passive magnetic field prior to DI stage, would the DI stages last longer or become more effective? I do not know if there is a change in energy required for covelant bonds to occur in a curated environment.

 

[soymilk]

The dwell time came from a discussion on if a slower contact time would be beneficial for silica. It was suggested that maybe running a 75gpd membrane would possibly be better than running a 200gpd system.

I’m not particularly worried about dwell time. The discourse transitioned right now to if it’s possible to still have silica even if your rodi displays 0.

it was to my understanding that silica can be neutral thus not really being affected by di resin. So some silica can make it thru your rodi while your tds meter still shows 0.

 

[Randy Holmes-Farley Verified Community Expert]

lol that’s how the discussion started. I recently changed and upgraded my DI after 5-6 months of setup (acid washed and bleached rock). Diatoms / Dinos came and never cleared. So, I was suspicious of my DI that had not shown any signs of depletion at all. It finally popped above 0 TDS and a spent DI system seems like a pretty good fit for unwanted algae growth.

Just to be clear, silicate isn't used by dino's.

Dwell time should not be a concern in any RO/DI since the RO limits the flow to slow enough and if the effluent is 0 ppm TDS, some silicate may get through, but not huge amounts. Adding a second DI in series will take out more, if it is an issue.

 

[Randy Holmes-Farley Verified Community Expert]

Furthermore, it was posed that if you could align (polarize) water molecules through an electrical or passive magnetic field prior to DI stage, would the DI stages last longer or become more effective? I do not know if there is a change in energy required for covelant bonds to occur in a curated environment.

I suggest you stop cruising the internet or you may end up owning the Brooklyn Bridge. lol

There are no covalent bonds formed or broken in an RO or DI, and the comment about orienting water molecules before they go into a DI is nonsensical.

A DI is a simple swap of ions on the DI (H+ and OH-) for ions not on the the DI (everything else that you want to remove). The released H+ and OH- combine to form water, with nothing remaining in the water except water.

No water orientation effects, even if they occurred (they do not) will impact the simple swapping of ions onto the polymer.

I discuss in great detail how RO/DI systems work here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

 

[Randy Holmes-Farley Verified Community Expert]

The dwell time came from a discussion on if a slower contact time would be beneficial for silica. It was suggested that maybe running a 75gpd membrane would possibly be better than running a 200gpd system.

I’m not particularly worried about dwell time. The discourse transitioned right now to if it’s possible to still have silica even if your rodi displays 0.

it was to my understanding that silica can be neutral thus not really being affected by di resin. So some silica can make it thru your rodi while your tds meter still shows 0.

It is certainly possible to have silica with 0 ppm TDS, as it is also possible to have other things.

0 ppm TDS, even if measured perfectly accurately, is not none. It means <0.5 ppm TDS.

That 0.5 ppm might be anything, and since the uncharged form of silicate (silicic acid) gets through an RO reasonably well, there can be a substantial amount in the DI effluent. Same is true for ammonia.

The uncharged form of silicate (silicic acid) is not the main reason it is more poorly bound by a DI, but rather the way the charge on silicate is spread out over multiple oxygen atoms and they way that spread out charge interacts with the charge on the polymer. That's a nitty gritty chemistry detail, but here's all that needs to be known by typical reefers (from my article above):

In the DI descriptions above, I did not address the fact that some ions will show a greater preference for attachment to the resin than will others. When the resins are not depleted, it does not matter what the ions’ affinity is, as all are bound. But in a depleted scenario, when there are more ions than ion binding sites, those with a higher affinity for the resin will be retained, and those with a lower affinity will be released. It turns out that silicate is found at the lower end of affinity for anion resins. Consequently, if the DI resin has been collecting silicate for a long period and is then depleted, a large burst of silicate may be released.

 

[RichReef]

Spectrapure sells a silicate cartridge. I forget the name of it.

 

[Randy Holmes-Farley Verified Community Expert]

Spectrapure sells a silicate cartridge. I forget the name of it.

Yes, so does BRS.
I personally think 2 DI in series is a better plan than buying a more expensive DI. When #1 depletes and reaches 50% of the TDS incoming to it, you swap the #2 into the #1 position, and that way can use all of the DI to a grater percentage of capacity.

 

[RichReef]

Yes, so does BRS.
I personally think 2 DI in series is a better plan than buying a more expensive DI. When #1 depletes and reaches 50% of the TDS incoming to it, you swap the #2 into the #1 position, and that way can use all of the DI to a grater percentage of capacity.

That's exactly what I do.

I never used the silicate one. Just saw it for sale.

 

[second_decimal]

lol thanks to the internet we can all be experts in our own minds pretty quick. Thanks for the feedback and clarification.

 

[Randy Holmes-Farley Verified Community Expert]

lol thanks to the internet we can all be experts in our own minds pretty quick. Thanks for the feedback and clarification.

You're welcome. That's exactly why the Reef Chemistry forum exists.

 

[TWYOUNG]

Is there a filter media that can remove silica that is already in the display tank?

 

[gbroadbridge]

Is there a filter media that can remove silica that is already in the display tank?

Sponges and diatoms

.. and GFO may help if it is not exhausted by Phosphate.

 

[TWYOUNG]

Sponges and diatoms

.. and GFO may help if it is not exhausted by Phosphate.

Guess I'll let the sponges and diatoms soak it up because I'm already struggling to keep phosphates up.