NSW with low ph and alk again...

[RoachF4]

Sometime ago I posted about this problem, never really came up with a solution, but it really didn't seem to be hurting anything so I let it go. I used Reef Crystals for awhile and constantly had low ph (7.8 to 8.0) and low alk (1.6 to 2.6) Salifert Test. I recently switched to the Salinity brand by Seachem just to try it out and I am having the same issue.

Mixed up a fresh batch yesterday and tested it today:
ph - 8.0
Alk - 6.8
Ca - 420
Mag - 1280

I use RO/DI (The Filter Guys) in a food safe 50 gallon drum. The solution is to buffer the NSW, but that seems like a waste of money. Isn't the salt mix supposed to mix up to the appropriate values. I don't know nearly enough about the chemistry involved, but is it possible that the ph and alk coming out of the RO/DI is so low that the salt mix can't raise it enough?

Today I spoke with a guy at the LFS and he is having the same problem with his NSW and having to buffer as well. Anyone else out there having issues?

Matt

 

[bertoni]

The alkalinity is a bit low, but acceptable. The low pH most likely is either a measurement problem (bad kits and calibration solutions are fairly common) or due to carbon dioxide. Another possibility is that the alkalinity kit is far off. What is the SG of the water, and was the measurement device calibrated with a saltwater reference solution?

The pH of the RO/DI output is irrelevant, since it has no buffering and will conform to the pH of the saltwater to which it's added.

8.0 is fine for pH, especially in houses with the windows shut up due to heat or cold. I wouldn't worry about it. If you want to track down what's happening, you could try aerating a sample outside for 3 hours and measuring the pH. It should rise quite a bit toward 8.3 or so.

 

[RoachF4]

The S.G. is 1.026. Well the alk was tested with Salifert and Lamotte, which I've been using for awhile now...they're not perfect but I think they are pretty close. The ph was tested though my Apex probe (recently calibrated). The values aren't bad, it's just weird that fresh batches of saltwater have such low values. Shouldn't they start out high and then lower over time? Thanks for your time with this.

Matt

 

[bertoni]

The pH is fairly common for saltwater kept inside. Is "NSW" natural sea water, or new salt water? In either case, the carbon dioxide content of the air is what sets the pH.

 

[RoachF4]

Sorry...it's new salt water. The ph isn't a big cocern, but the low alk is a little troubling. Is it common practice for people to buffer their new batches of salt water? It's also possible that I have two bad test kits, that are both reading low. I'm really wondering if anyone else is having this issue...low alk and/or ph with new salt water? If so are you using Salinity by Seachem? I really like the stuff so far...Thanks for your time Bertoni.

Matt

 

[HighlandReefer]

The pH of your salt mix is not a concern. When you add it to the tank, things equilibrate out. As Jon noted providing the alk is at normal levels, the CO2 content is what causes this. Aerating the salt mix well can help get the extra CO2 out.

As far as your low alk, perhaps precipitation is occurring in your salt mix during mixing. When the precipitants form, this will use up alk and some calcium. Adding the salt mix slowly between vigorous stirring can help prevent precipitation from occurring.

It is not usually recommended to increase your alk level in a salt mix but to increase the alk level with baking soda in the tank. However your salt mix is low in alk, so perhaps using baking soda in your salt mix using the Chemistry Calculator to determine how much may work without much precipitation.

Reef chemicals calculator
http://reef.diesyst.com/chemcalc/chemcalc.html

 

[bertoni]

I agree that precipitation might be an issue. The salt mix might have separated some in shipping, too, which might be fixable with some stirring. I'm not sure what it's that low.

 

[wayne in norway]

How do you measure salinity? How did you calibrate the instruement. I'd also advise stirring the salt thoroughly in the bucket as it might have settled. Don't roll the bucket - that just makes it worse. If you look at alk and Mg alone you're jsut a little bit weak, and Ca is just at the bottom range of what the manufacturer states.

The lack of alk in the RO is a nonissue, otherwise everyone with RO would need to do the same, and we don't. There is (almost) no alk in RO, and that's what is expected.

I would guess that the Reef Crystals had gotten damp at some point, and precipitation in the bucket will kill the alk to the levels you describe. You don't need to even spill water into the bucket to do it, just leavign the lid loose in a damp room is enough to do it.

 

[wayne in norway]

Oh, and I assumed NSW meant natural seawater as well. What you describe is more normally described as fresh, or freshly mixed rather than new.

 

[RoachF4]

OK..thanks for the replies. I appreciate the suggestions. Currently I mix RO/DI with the new Seachem brand of salt mix (the one where they have the values of each batch printed on the bucket). I use an old RIO 2100 in a 50 gallon drum. I do leave the lid on (but there is a hole) the drum to keep out debris and bugs becuase it's in the garage. SHould I try mixing without the lid and placing an air stone in the drum?
Also, when I said they I buffered the "freshly mixed salt water", I used Bulk Reef Supplies "recipe 2" and their calculator to bring it up to an acceptable range. Thanks again.

Matt

 

[bertoni]

I think the air stone will just make a mess. I might try adding the salt more slowly. If that doesn't help, I'd check the pH of the water as it's being mixed.