RODI set up separate canisters not sure

[chicago]

ok so for years i used just mix bed. now i setup a three part. anion-) cation-) mixed bed.

odd thing is the mixed bed appears to be used up faster than the anion. ? Take look at these pics. first one is anion. second cation third and forth to the right are mixed

 

[Randy Holmes-Farley]

Assuming it is plumbed correctly in the order you mention, I'm not sure why the mixed bed is depleting faster. The anion and cation resins will have higher capacity than the mixed bed, but still the amount getting through both an anion and cation to the mixed bed should be small unless water is channeling through them.

Double check, if you can, that you have one anion and one cation and not two anion or two cation before the mixed bed.

 

[chicago]

Randy.. thank you for the response.. I was hoping you would see this post.. I actually have the spectra pure double ro system (7 stage)... I then added on to after that my old kent.. yes kent for use of just the three cartridges if I wanted.. I had room on the wall for those that might wonder why... anyways.. back to this thread. I will refill them all today and see how things go over the next week or so... I do believe they were all filed properly... i have the pro mixed bed as well as the regular mix bed... both change colors... both are from DRS as is the Anion and Cation resins... I have Chicago water ..or should say north suburbs of Chicago water which is lake Michigan water. Anion -> Cation _> Pro Mixed Bed (cation changing) - > Regular mix Bed..

Randy - which one and what order would you suggest for the mix bed after the anion-Cation-
pro or regular mixed bed (or one or the other...

If I recall correctly in the reg mix bed (not PRO) its the Anion blue beds that change color and on the
PRO - its the Cation Purple beds that change color from purple to amber.
in other words
Reg Mix Bed- anion is the changing factor blue to amber
Pro Mix Bed- Cation is the changing factor purple to amber

Pulling my hair out why not working... back in a week or so and perhaps with Randy's Help I can get this figured out.. Thanks

 

[Randy Holmes-Farley]

Randy.. thank you for the response.. I was hoping you would see this post.. I actually have the spectra pure double ro system (7 stage)... I then added on to after that my old kent.. yes kent for use of just the three cartridges if I wanted.. I had room on the wall for those that might wonder why... anyways.. back to this thread. I will refill them all today and see how things go over the next week or so... I do believe they were all filed properly... i have the pro mixed bed as well as the regular mix bed... both change colors... both are from DRS as is the Anion and Cation resins... I have Chicago water ..or should say north suburbs of Chicago water which is lake Michigan water. Anion -> Cation _> Pro Mixed Bed (cation changing) - > Regular mix Bed..

Randy - which one and what order would you suggest for the mix bed after the anion-Cation-
pro or regular mixed bed (or one or the other...

If I recall correctly in the reg mix bed (not PRO) its the Anion blue beds that change color and on the
PRO - its the Cation Purple beds that change color from purple to amber.
in other words
Reg Mix Bed- anion is the changing factor blue to amber
Pro Mix Bed- Cation is the changing factor purple to amber

Pulling my hair out why not working... back in a week or so and perhaps with Randy's Help I can get this figured out.. Thanks

I would always have a mixed bed last. The reason is that the effluent from an anion or cation only bed will be very high or low in pH, where the mixed bed will not (unless it is depleted).

I'd also put the cation bed first to remove magnesium and calcium (which is the usual recommendation). If you had an anion first, then if those two are high enough, you might precipitate them in the high pH inside the anion resin.

I don't have an opinion on which mixed beds come before another mixed bed, except that I'd put the cheaper one first since it will deplete far faster. Alternatively, you can use the same brand for both, and when the first one depletes, move the second one tot eh first position, and the new one in second position. That allows full use of each mixed bed with no waste of any capacity (that's what I did).

 

[chicago]

yep.. thanks for the confirmation.... I read somewhere to use Anion first not sure where.. I think it was where someone just used a Anion bed then mix bed cation.... anyways.... i do switch out the last two (the mix BED ) cartridges when one appear to be almost exhausted.. I do have a question on that.. is there any truth that the DI resin will leach out what it took out ?

 

[chicago]

by the way.. I am ok with a high ph RO water..... if so what would you suggest thanks Randy

 

[Randy Holmes-Farley]

yep.. thanks for the confirmation.... I read somewhere to use Anion first not sure where.. I think it was where someone just used a Anion bed then mix bed cation.... anyways.... i do switch out the last two (the mix BED ) cartridges when one appear to be almost exhausted.. I do have a question on that.. is there any truth that the DI resin will leach out what it took out ?

A depleting DI resin will start to swap out weakly bound ions inside of it and bind more strongly bound ones coming into it, so yes, ions will come out.

This is more of a how it works than a recipe for setting one up, but this has a lot more info:

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

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.

Other complications can also impact resin depletion. One potentially important issue is that the anion and cation-binding sites may not become depleted at the same time. Figure 10 shows this scenario when both types become depleted together, with sodium and chloride in the effluent. But, it is possible for one to become depleted first, and in that case, the pH of the effluent can swing far from neutral. Figures 11 and 12 show what happens when a lot of carbon dioxide is present, as is the case with some well waters. Initially, it is mostly bound as bicarbonate, and the effluent is essentially pure water. Note, however, that as the bicarbonate is removed, the anion binding resin is being taken up with bicarbonate, while the cation-binding resin is unchanged and is therefore not being depleted.

 

[Randy Holmes-Farley]

by the way.. I am ok with a high ph RO water..... if so what would you suggest thanks Randy

Ignore it.

from the above:

[[As an aside, my RO/DI effluent always seems to have a high pH (9-10) even before its conductivity rises significantly. While there are many complications to measuring pH in pure water, where pH kits and meters do not function well, I cannot so easily dismiss these readings as being purely artifact, although they may be. I have wondered for years what might be causing it, and have not yet found any clear answer. However, if the above process is happening in my system even on a small scale, it might explain the results (my tap water contains chloramine). A sodium hydroxide solution with a pH of 9 has only 10-5 moles/L of sodium hydroxide, or 0.4 ppm sodium hydroxide by weight. Is that all or part of the high pH that I observe in my effluent? I’m not sure.]]

Final Effluent pH

Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:

1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.

2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).

 

[chicago]

Thank you for that info again..... this is why I keep two going at the end and why I added in my old kent.. just to have a grab all mix bed at the end of all of it.. At one time I was putting GFO in one of these.. to only find out my test kit was off since it was testing Phosphate in Fresh Water.. sorry for the diversion... Thanks again Randy