Remove DI Resin to up PO4, NO3?

[Pyrosteve]

I asked this in the Dino thread too. Will removing/bypassing the Deionization resin and just using RO water for top-off up my Phosphates and Nitrates? Any harm to the RO/DI unit or to any tank livestock doing this? Sediment, Carbon and RO would still remove heavy metals and chlorine/chloramines, correct? I know normally this would not be a good thing but I bottomed out my PO4 and NO3 adding too much GFO and now I have Amiphidium Dinos. Silicates would also be good since one theory is to out compete them on the sandbed with a diatom bloom.

 

[Dkeller_nc]

Probably not, but it greatly depends on your tap water source. Some municipal water sources contain a substantial amount of nitrates/phosphates, but that's somewhat unusual.

Personally, I would not alter my RODI unit for the purposes you describe; I'd much rather have control over the tank parameters by purchasing some sodium nitrate and sodium phosphate, and simply dose them to bring the NO3/PO4 concentration of the tank back up. Alternatively, you can simply remove any GFO/GAC from the tank's filtration train, and fish feeding will lead to a gradually increasing concentration of those nutrients in the water.

 

[Pyrosteve]

Probably not, but it greatly depends on your tap water source. Some municipal water sources contain a substantial amount of nitrates/phosphates, but that's somewhat unusual.

Personally, I would not alter my RODI unit for the purposes you describe; I'd much rather have control over the tank parameters by purchasing some sodium nitrate and sodium phosphate, and simply dose them to bring the NO3/PO4 concentration of the tank back up. Alternatively, you can simply remove any GFO/GAC from the tank's filtration train, and fish feeding will lead to a gradually increasing concentration of those nutrients in the water.

Thanks. I've taken my GFO/GAC off line and have upped my feeding. I just watched the BRS videos on RO/DI and it seems like this might be possible and work for me (if I understand it correctly). I would need to run Cation resin only to remove positively charged ion contaminants (ammonia, iron, sodium) and not use Anion resin to allow negatively charged ions (PO4, NO3 and Silicates) in the water BUT like you said, it depends on my municipal water. I'm using a single mixed bed DI now so it's probably not worth doing. It just seems like a waste to remove elements only to add them back.

 

[Dkeller_nc]

I honestly wouldn't bother. The main reason that we use RODI systems is for control, and to prevent slow salinity rise over time by adding top-off water that contains ions. That control is valuable - with a properly functioning RODI system, you know without doubt that everything that might be harmful to your tank's inhabitants is being removed, even though you're "adding some things back" when you dissolve salt into it for a water change.

If you don't feel like messing with dissolving up your own sodium nitrate and/or phosphate for use in the tank, a fair number of folks seem to have success with Seachem Flourish Nitrogen and Seachem Flourish Phosphate. One caution, though - as I understand it, these products are the potassium salt of the respective nutrient (i.e., potassium nitrate and potassium phosphate). So you won't want to use large amounts of them or over a long term period without water changes, as highly elevated potassium levels in a reef is toxic to the tank's inhabitants.

 

[Reefahholic]

;Muted

 

[Randy Holmes-Farley Verified Community Expert]

I would not remove the di. My main reason to use it in the first place is copper.

 

[Pyrosteve]

I would not remove the di. My main reason to use it in the first place is copper.

Ok. So bad idea then to completely remove the DI. I thought copper was removed by the carbon block and RO membrane.

I don't think I'll go this route but just out of curiosity, if copper is positively charged, would using just Cation resin remove it?

 

[Dkeller_nc]

Ok. So bad idea then to completely remove the DI. I thought copper was removed by the carbon block and RO membrane.

I don't think I'll go this route but just out of curiosity, if copper is positively charged, would using just Cation resin remove it?

In theory it is, especially by the RO membrane. However, an RO membrane is a percentage rejection process (i.e., 98% rejection is commonly advertised by Dow with their Filmtec membranes). And copper is toxic in very small amounts - depending on the study, possibly in the parts per billion range. And if it's continually added to the tank in the form of top-off water, it will gradually build up in the tank, which isn't good.

And yes, a cation exchange resin will remove positively charged ions, including copper. However, one typically doesn't see just one side of the cation/anion exchange resin employed, because doing so alters the acidity/alkalinity of the water flowing through it, at least if the cation resin is in the protonated form and the anion exchange resin is in the hydroxyl form. An exception are water softeners which commonly include only cation resins, but those resins are in the sodium form, not the protonated form.

 

[Randy Holmes-Farley Verified Community Expert]

As mentioned by dkeller, if you use just a cation resin the pH of the effluent be very low and will deplete tank alkalinity.

 

[Pyrosteve]

Ok. Thanks for the explanation. I think I understand . So by using just the cation exchange the water is made acidic and without the anion exchange to remove it, an additional buffer would be needed. Sounds like more trouble than it's worth.

 

[Randy Holmes-Farley Verified Community Expert]

Ok. Thanks for the explanation. I think I understand . So by using just the cation exchange the water is made acidic and without the anion exchange to remove it, an additional buffer would be needed. Sounds like more trouble than it's worth.

Right. The cation resin swaps all incoming positively charged ions for H+. With an anion bed around, an identical number of OH- are released, which combine to form H2O. Without the anion resin, the H+ remains in the water.