Concerns with Well Water pH after RO/DI

[Amoo]

I have a degree in Nuclear Engineering, it's been a while since school, but feel free to talk dirty to me.

As the title states, I have well water and an RO/DI unit on order. Last night I got to thinking that most tap water is usually basic, but because of where I live I had the thought that my well water might be acidic. After testing I was correct, well below 6.0, like well below. If 6.0 is orange, strip was yellow. We had a water quality test done a while ago to test the contents, but I can't locate it at the moment to give the exact value.

My concern is what is my pH going to look like after RO/DI? IIRC they tend to exhaust their resin and start to release basic water, which would tell me the units are seeded with acidic particles. Hopefully I'm getting my theory backwards and somebody can correct me, but it would be nice to know if I'm going to need something to adjust my pH before I get everything here and start dumping water into my tank for it's cycle.

Thanks,

Moo

[Randy Holmes-Farley]

The pH after the DI is irrelevant and unmeasurable for you (at least until it is depleted).

BUT, if your well water has significant CO2 in it (lowering the pH), that can deplete the DI pretty fast as CO2 gets through an RO membrane fairly readily. You can get a test kit to measure the CO2 from Spectrapure.

I discuss the pH issue here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

from it:

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).

[Amoo]

You're my hero Randy, that's all I'm saying. I asked for dirty and you provided. Nerd-gasm.

[Randy Holmes-Farley]

:lol:

You're welcome.

Happy Reefing. :)

[Amoo]

Ok Randy, here's one straight up your alley. I was able to locate my water analysis report:

pH 5.7
Calculated Hardness 5ppm (I assume this is TDS?)
Ca .8ppm
Cu .17ppm
Mg .7ppm
SiO2 9.24ppm
Na 4.2ppm
Zinc .36ppm

The following parameters were tested and came back as negligible:
Al, As, B, Cr, Fe, Mn, Mo, Ni, P, K

Here is my takeaway from this water report, and hopefully you can fill in or correct my misunderstandings. The only two levels I would need to be concerned about are definitely the Copper, and possibly the Silica. If I'm not mistaken, the Copper can be filtered out with Carbon. I'm honestly unsure of the effects on a reef tank with the Silica, but nothing else jumped out at me.

My question from this point becomes this, am I actually in a situation where I would need an RO/DI Unit? Obviously the worse thing I could do, would be to introduce copper into my system, so I would have to remove the Cu.

My thoughts would be, initial tank setup done with RO/DI water. Remove DI filter and maintain 5 gallons of RO water for daily top offs. Keep 14 Gallons of well water, salt mixed, heated, aerated and running on carbon for the week, perform weekly water change, repeat.


The reason I'm trying to outsmart the basic, just go with RO/DI reason is two-fold. One it's obviously cheaper if I can use what I currently have. That's not the most important one though. As you might know, well pumps aren't meant to operate much beyond 50psi. Well RO/DI units aren't exactly happy with ~40 psi on average and I can easily see myself burning out my well pump needing to run it for 8 hours at a time, just to perform a weekly 15% water change on my tank.

In fact, my RO/DI unit is 100GPD and wants to have a minimum 60PSI inlet pressure, so realistically, I'm in a situation where even using the unit itself would cause me to add a booster pump, which I'm willing to do, but that still doesn't solve the issue of possibly overheating my well pump itself.

[Randy Holmes-Farley]

I wouldn't be comfortable expecting carbon to remove the copper (the 0.17 ppm is the copper?).

I dose silicate, but that 9 ppm is huge and you'd want the DI for it too or else diatom problems might result.

For a normal situation (no pump issues) I'd use RO/DI and the DI will last a very long time because the water total ions is very low. With this situation, you might consider DI alone. You'll run through it a lot faster, but your total ions are not all that high.

[Amoo]

I didn't realize that just the DI alone would filter out the Copper as well as the Silica?

[disc1]

That zinc is another metal you definitely don't want.

You can get a booster pump to help with the water pressure.

[Amoo]

I'm not discounting your knowledge here disc, but according to this article, the zinc may not have much of an effect considering my small dosage?:

http://www.reefcentral.com/forums/showthread.php?t=1940807

[disc1]

I don't know the toxicity level, but I'd still be concerned that it would accumulate.

[disc1]

The info in that thread indicated zinc was tested up to 500ppb. The op water has 360ppb. So he's almost at that tested limit now.

[dkeller_nc]

A couple of comments with respect to your specific situation:

You may not want your household water at that pH for reasons other than anything to do with your reef tank. Acidic tap water tends to dissolve metals out of plumbing and plumbing fixtures. Depending on the age of your house, the plumbing can contain lead, iron, chromium, copper and other metals that, depending on their concentration, you may not want to be drinking.

From the standpoint of your reef tank, you've a very special situation that might allow you to operate an RODI system much more efficiently than the standard 4 to 1 waste to product ratio. The problem with operating a typical hobbyist system at a 2:1 or a 1:1 ratio is exceeding the silica and calcium solubility in the water on the waste side of the membrane. That will cause precipitation of insoluble silica and calcium salts on the membrane surface and quickly render it impermeable.

However, with your incredibly low dissolved solids content, it may be possible to operate an RODI system at a 1:1 waste to product ratio or even lower without getting anywhere near the solubility limit of common calcium and silica compounds.

[bertoni]

I didn't realize that just the DI alone would filter out the Copper as well as the Silica?
DI will take out anything that's reasonably strongly charged, including copper ions and at least some silicate.

[Randy Holmes-Farley]

You, optimally, don't want zinc over about 40 ppb in the tank. I discuss zinc toxicity here:

http://www.reefcentral.com/forums/showthread.php?t=2404936

[Amoo]

Thank you very much to everybody who has taken the time to help out with this unique situation. It looks like I'm going to need to do a couple of things here. First would be, buy a booster pump. If I can spend hundreds of $s on stuff for a fish tank, there is no reason I shouldn't have spent a few hundred $s a while ago to increase household water pressure. I'm going to get the added benefit of being able to run my RO/DI, but as a 32 year old married guy with a 16 month old, my house comes before my hobbies.

I'm now also looking into the possibility of getting an acid neutralizer, possibly this unit: Acid Neutralizer (http://www.midatlanticwater.net/shop/acid-neutralizers/12x52-non-backwashing-acid-neutralizer-package-free-calcite) . I'm going to assume this isn't going to have a negative impact on my water, since this system uses a calcite media and that should bring up my pH levels a bit.

I know my home is all PVC piping with a few old iron pipes (home was built in the 20s, then moved to it's current location). This tells me my silica and Cu are coming from the ground (I think).

The RO/DI unit that I currently have is 3 stage with an additional DI canister. Water comes in the sediment cartridge (which I don't need), travels through a carbon cartridge (which I don't need), into the RO Membrane (which I still need maybe), then finally passes through a DI canister and goes out to clean water (supposedly).

This leads me to wonder if I shouldn't disassemble my Carbon filter and fill it with 500ml Cuprisorb, run inlet line into the Cuprisorb canister, then through the DI resin, then to my mixing tank.

From what I can tell on my RO unit there doesn't appear to be a way to affect the discharge rate manually. So if I were to still use an RO unit, I may have to get one that would let me manually adjust the discharge rate. Something along the lines of this might be ideal for my situation:

Spectrapure 2:1 w/ High Silica Buster (http://spectrapure.com/AQUARIUM/RO-DI-SYSTEMS/CSPDI-RO-DI-Systems/CSPDI-Manual-Flush-180-GPD-RO-DI-System)

Combined with this:

Booster pump Kit (http://spectrapure.com/Automatic-Flush-System-Booster-Pump-Kit-for-SpectraPure-60-90-180gpd-Auto-Flush-RO-RODI-Systems?filter_name=SpectraPure%E2%80%99s%20auxiliary%20High-Flow%20Booster%20Pump%20Kit%20P/N:%20BPHF-AF-115)

I'm not quite sure I'm getting much out of the carbon and sediment filters included, but anything less than that model, I can find that includes both RO and DI seems to have a worse waste ratio. So in my case, I might be best to pony up the ~$400 for a very high flow (180gpd), high efficiency (2:1 wastewater) and call it a day.

[Randy Holmes-Farley]

The RO/DI will totally remove copper, so I wouldn't go the cuprisorb route.

[Amoo]

Yes, that was kinda of an option 1, cuprisorb canister + di without current RO membrane or option 2 just pony up for the more expensive RO/DI unit with higher flow rate.

Option 1 wastes less water but might not be good enough filtration

Option 2 hurts the pocket book more and wastes more water, but might be my safest bet.

[dkeller_nc]

you don't need the cuprisorb, nor would I take out the carbon cartridge, you just won't have to change it very often compared to us schmucks that have to remove chloramine. It's still useful to remove some types of organic compounds that your RO membrane and DI cartridge might not.

From the standpoint of affecting your discharge rate, this is quite easy. You simply disassemble the RO membrane holder, remove the waste tubing fitting, and remove the internal restrictor. You then replace it with an external restrictor that you can purchase from Bulk Reef Supply or Buckeye Hydro.

[Amoo]

Thanks dkeller nc, I looked to see what you were talking about and it looks like my unit already has a 800 flow restrictor on it, which means all I should need to do would be to disassemble the parts in the membrane holder and I would be gtg.

[Uncle Salty 05]

Before getting an RO/DI unit I used one of these with great success:

http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=4484

My tap water is around 110 TDS and one of these cartridges would produce 125-150 gallons of zero TDS water before the TDS would begin to rise.
If your well water has very low TDS to begin with one of these might be worth looking into. They are just a small carbon block and DI resin.
You can hook it directly to your kitchen faucet and there is no waste water produced at all. Pressure is not a factor either, actually low is probably better.

[Amoo]

Wow, that thing is pretty damn sexy and might have my name written all over it, Thanks Uncle Salty. I'll have to mull things over and weigh the cost of all solutions. Mind if I ask, why you decided to just end up getting a RO/DI afterall?

[Uncle Salty 05]

You're welcome.
I have a 180, a 55, a 20 long and a 10 gallon.
Plus I used to do aquarium maintenance as a part time job.
At 110ppm I was burning through those cartridges pretty quick. Now with the RO unit my DI resin lasts a lot longer.