To Aerate or not RO/DI

[korbynlehr]

<a href=showthread.php?s=&postid=8303163#post8303163 target=_blank>Originally posted</a> by Robs26reef
Well I just did some research and found out it is very important to aerate RO water before mixing the salt vigorously for 12-24 hrs before adding synthetic salt mix. RO/DI filters do there job very well. so well that the remove virtually all dissolved minerals and produces water that leans toward the soft, acidic side. Aeration helps increase the alkalinity. and in turn its ability to resist a change in pH in the presence of an acid-prior to mixing in the salt. if not aerated the buffers in the synthetic salt would be quickly used up. then your pH will be unstable. So I have been doing it wrong for 4 years now. nice to know.

Randy,
What is your take on the "proper" way to mix ro/di with our without aerate?

[jdieck]

Randy is out for a while but let me try to check on that statement that IMO has a couple of assumptions that do not seem correct, first of all, RO/DI water has no buffering capacity at all as it does not contain any minerals, as such, it's PH is irrelevant because as soon as you add any buffer the PH will adjust.
Having said that O/DI water exposed to air will contain dissolved CO2 which may give the perception that it is acidic but as I mentioned without buffering capacity that is not an issue. Aereating the RO/DI water will increase the dissolved CO2, there is no way aereation alone can increase the water alkalinity as you need Bicarboante and Carbonate ions to do that and there are none in the air. (Well unless you leave next to a query that blasts 10 times a day and your air is so dust poluted that will add some of that :D)
In any case, one of the most usual mistakes is to dump the salt into the water and then start mixing. When the undissolved salt settles in the water there is zones of very high localized PH which will cause the Alkalinity and Calcium buffers to precipitate into carbonate thus leaving the unsoluble residue.
The best way to mix is to start a large powerhead to have as much agitation as posible as well as a couple of airstones, add the salt to the water slowly and distributed across the water surface to prevent any localized concentration.
COntinue agitation and aereation for 24 hours to achieve good chemical stability.

[Boomer]

Nice post jd :D

[cayars]

Actually if the powerhead you are using has the airline connection (many do) then you can hook an airline up to this and let the powerhead blow your bubbles for you and you won't need the airstone.

I typically fill a 35 gallon trashcan with RO/DI water and as soon as the water level is about 6" I start the powerhead and turn on the heater. When the water level gets to the top of the trashcan I add my buffer. After an hour or so I slowly start adding my salt in over a hour or so period to allow it to mix well. I then leave it circulating with the powerhead for a day if possible before using it for good measure. I then do a couple of tests on the water before adding it to my tank to make sure I didn't get a bad batch of salt. :)

After using the water I start my next batch so I have it ready when ever needed or for an emergency (ie line comes off a pump or reactor and dumps 20 gallons on the floor - has happened).

Make sure temp is within 2 degrees and salinity is correct (of course).

When filling my tank (water change) I connect a tube (actually always connected) to the powerhead in the trashcan and feed it near the bottom of my tank on the opposite side of the tank from my overflow. I route the overflow to my discard water trashcan and start the powerhead/pump in my fresh mixed water trashcan. As the powerhead adds my new water the corresponding amount of water goes out the overflow into my discard can keeping my water level constant in the tank. I can then keep all powerheads and other equipment running (except return pump/skimmer) while doing the water change and the fish/corals have no idea a water change just happened and don't get stressed.

The only downside to my method of water change is that some of my new water will make it out the overflow/discard as it gets mixed with my tank water. The amount will be proportial to the water change if the powerheads do a good job but this is well worth it in my oppinion.

Carlo

[korbynlehr]

Okay, here is another question.
When I add my salt to the RO/DI is it okay to add the B-ionic alkalinity part in there also?

[jdieck]

<a href=showthread.php?s=&postid=8574953#post8574953 target=_blank>Originally posted</a> by korbynlehr
Okay, here is another question.
When I add my salt to the RO/DI is it okay to add the B-ionic alkalinity part in there also?
Yes but not at the same time.
In other words, mix the salt, after it is fully dissolved test the parameters, use the calculator to determine how much of each part to add to reach your targets for Calcium and Alkalinity. Over time you will notice that if the salt mix is consistent you end up adding the same amounts every time, is this happen then no more testing or calculations just add the amounts to adjust and then you can add them before or after the salt is added but not at the same time.

[J. Montgomery]

"if not aerated the buffers in the synthetic salt would be quickly used up"

Am I wrong in thinking that this statement is incorrect, and that a buffer can NOT be used up? Just wanted to check.

[jdieck]

<a href=showthread.php?s=&postid=8576258#post8576258 target=_blank>Originally posted</a> by J. Montgomery
"if not aerated the buffers in the synthetic salt would be quickly used up"

Am I wrong in thinking that this statement is incorrect, and that a buffer can NOT be used up? Just wanted to check.

Yes, that statement is absolutely incorrect. Pre-aereation of RO/DI water has nothing to with wether the buffers will be used up or not. On the contrary as I mentioned, if you aereate the RO/DI water you will be increasing the amount of dissolved CO2, that dissolved CO2 will react with the calcium oxide and calcium hydroxide buffers in the salt to precipitate some carbonate, small amount but that will reduce the alkalinity and calcium in the final water mix.
This is the same reson you do not want to aereate a Kalk solution. The CO2 in the air will degrade the solution to form calcium carbonate precipitate.

Having said that, aeration during or after mixing will aid speeding up the stabilization of the chemistry. Once the right ionic balance is achieved the addition of dissolved CO2 will help equalize the CO2 content with that in the air thus stabilizing the mix PH before the mix is added to the aquarium. For aquarium stability you prefer this stabilization happening in the mixing tank, this is why I recommend aereating the water during or after the mix has been dissolved, not before.

Once the mix is stable, ions will not be afected regardless if you achieved stabilization by aereation, agitation or simple holding time.

From the article linked below:

In order to minimize the formation of insoluble carbonate salts when mixing, the following suggestions may be helpful:

1. Add the salt to a full batch of water, rather than adding water slowly to a large batch of salt. The latter allows a greater time at much higher than natural seawater salinity, which may tend to precipitate calcium and magnesium salts.

2. Stir the mixture vigorously as it is being dissolved.

3. If using a mix with a high initial pH, aerate the mixture as well as stirring it. The aeration will reduce the pH.

So to understand this correctly, the idea by aereating the mixture while stirring it is to reduce the PH of the mix to reduce carbonate precipitation. Aerating the RO/DI ahead of time will do nothing but waste your time as the high PH is formed by the salt mix, not by the RO/DI.
Many salt mixes will not have initial high PH, for those aereation will not be that critical

What is that Precipitate in My Reef Aquarium?
http://www.reefkeeping.com/issues/2005-07/rhf/index.php

[mwitten]

<a href=showthread.php?s=&postid=8570699#post8570699 target=_blank>Originally posted</a> by jdieck

In any case, one of the most usual mistakes is to dump the salt into the water and then start mixing. When the undissolved salt settles in the water there is zones of very high localized PH which will cause the Alkalinity and Calcium buffers to precipitate into carbonate thus leaving the unsoluble residue.
...


OK, not sure how I went this long without figuring this tidbit out. Makes a lot of sense, and explains a few things....

Thanks jdieck!

-Mike

[jdieck]

Enjoy!

[Randy Holmes-Farley]

I'll just pipe and agree in that there is no reason to aerate RO/DI before adding salt. Aeration after adding it is a fine way to add O2 and equilibrate the pH (by equilibrating CO2) if the pH is unusually high or low (although if you have excessive CO2 in your home, the pH may drop lower than you'd like).

[korbynlehr]

Randy,
So you are saying it is not neccesary to aerate ro/di?

[Randy Holmes-Farley]

Correct. :)

[jdieck]

<a href=showthread.php?s=&postid=8584387#post8584387 target=_blank>Originally posted</a> by Randy Holmes-Farley
I'll just pipe and agree ........

Everything I know, I owe it to my master :D

Well at least related to reef chemistry.

[Randy Holmes-Farley]

Uh oh, that's not good. :D

[jdieck]

<a href=showthread.php?s=&postid=8592515#post8592515 target=_blank>Originally posted</a> by Randy Holmes-Farley
Uh oh, that's not good. :D

:lol: