When TDS from our RODI starts creeping up???

[muttley000]

What are the first particles that make it through? Is this based on size or some chemical property. Just curious because it seems like people get all worked up when the TDS gets up to 5 or so. I'm thinking this may not be a big deal based on what the 5 represents. If it's calcium (I doubt we would be this lucky) who cares, if P04 "gets through" first I can see the issue.

[skunkmere]

i have data on RO permeate analysis and what pops out higher than everything else is sodium.

[jeff@zina.com]

I don't really care what it is, it means the DI resin is exhausted. Simple and cheap enough to replace.

Jeff

[philipph]

http://reefkeeping.com/issues/2005-05/rhf/index.php
i think you will find the answears you want here

[HighlandReefer]

Specifically from the posted article above:

"Several issues arise relating to the depletion of the DI resins that aquarists need to be aware of. Primary among these is that when a DI resin becomes depleted, that does not simply mean that the water passes through just as it came from the RO effluent. It may actually be much worse from an aquarist’s perspective. The reason for this is that while the DI resin is functioning properly, all ions will be caught. But when it is depleted, not only the new ions are coming through and might show up in the product water, but so are all the ions that ever got into the DI resin in the first place. The total concentration of ions coming out of the exhausted DI resin will not be raised as compared to the RO's effluent, but which ions are released may be very different.

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.

Perhaps even more of a concern is ammonia. In a system with chloramine in the tap water, the DI resin will serve the important function of removing much of the ammonia produced by the chloramine breakdown. Ammonia has a poorer affinity for many cation-binding resins than do many other cations (e.g., calcium or magnesium). Consequently, when the DI resin first becomes depleted, a big release of ammonia from and through the DI resin is likely. I recently had a DI resin become depleted, and the effluent contained so much ammonia that I could easily smell it."

[muttley000]

Interesting, Thanks for the replies!

[Buckeye Hydro]

Monovalent ions are released from the DI first - Randy mentions two above: silicate and ammonia.

[zigzag1]

Specifically from the posted article above:

"Several issues arise relating to the depletion of the DI resins that aquarists need to be aware of. Primary among these is that when a DI resin becomes depleted, that does not simply mean that the water passes through just as it came from the RO effluent. It may actually be much worse from an aquarist’s perspective. The reason for this is that while the DI resin is functioning properly, all ions will be caught. But when it is depleted, not only the new ions are coming through and might show up in the product water, but so are all the ions that ever got into the DI resin in the first place. The total concentration of ions coming out of the exhausted DI resin will not be raised as compared to the RO's effluent, but which ions are released may be very different.

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.

Perhaps even more of a concern is ammonia. In a system with chloramine in the tap water, the DI resin will serve the important function of removing much of the ammonia produced by the chloramine breakdown. Ammonia has a poorer affinity for many cation-binding resins than do many other cations (e.g., calcium or magnesium). Consequently, when the DI resin first becomes depleted, a big release of ammonia from and through the DI resin is likely. I recently had a DI resin become depleted, and the effluent contained so much ammonia that I could easily smell it."

Awesome infomation here.. something I have always been curious of. Exactly why I keep coming back to RC after so many years.

Thank you Cliff!

[HighlandReefer]

You're welcome. ;)

[disc1]

Monovalent ions are released from the DI first - Randy mentions two above: silicate and ammonia.

Silicate is NOT monovalent. It's quadrivalent. Softer ions come off first, those with the lowest affinity for the resin. Harder ions, those with a higher charge density, are able to replace them.

[tmz]

Bottom line ,post di tds is more of a worry than post memebrane tds as concentrations of low affinity stuff ,some of which is harmfu,l will come free in high proportions.

Using two(mixed resin) di chambers with a tds meter in between them helps prevent this and optimizes the efficient use of resin as well. The tds meter can tell you when tds form the first canister is higher than 0. When it is the second canister will clean it up. Changing the resin in the lead canister and rotating it with the second keeps things nice and clean. You don't have to guess when the resin is exhausted this way and can avoid premature changing.

[Buckeye Hydro]

Silicate is NOT monovalent. It's quadrivalent.

I should have paid more attention during chemistry class!

Russ