Chemistry Changing in my SW Container

[Jgoal55]

Hi all, posted this in my local forum but a couple of guys suggested I post here as well...thx.

In my never ending quest to get my nightmare nano under control, I decided to test my reservoir of SW. I typically mix about 50 gallons worth ahead of time and use it over the course of 2 months or so. I've been doing water changes this way for years, never a problem. And I still don't think this is the cause of my issues but I'm turning over every rock here.

Anyway, I've noticed that the chemistry of the SW in my reservoir changes over time. I'm using Reed Crystals salt. Here are the latest results all mixed at 77-78 degrees:

Jan 31 - New batch (tested the next day)

Alk - 10.06
Calcium - 420

2/9

Alk - 8.4 Alk
Calc - 420

2/16

Alk- 7.9
Calc - 400

As far as I understand, the water chemistry in SW shouldn't vary much as long as you have it circulating, which I do. Any ideas? Suggestions?

Only thing I can think of is that because I have loose fitting lid on the container, condensation from the evaporated water drips back into the tank. But no way that can cause these fluctuations right?

[bertoni]

I'm not sure why the calcium and alkalinity are precipitating. The pump might be encouraging precipitation by raising the temperature a bit. What brand of salt is this, and what is the temperature range of the reservoir? High temperatures can be a problem.

[Jgoal55]

Thanks. It's IO Reef Crystals.

The temperature ranges from 76-78 and stays pretty steady there. On really hot days in the summer down here (Miami) it can hit 80. But I usually hook a fan up to it in the summer. During our "winter" however, the temps stay pretty stable.

[tmz]

Well, the calcium drop of 20ppm is more or less in line with the alk drop of 2.16dkh. 20ppm of caclium is about what is used for 2.8dkh in calcium carbonate precipitation. So it must be precipitating; I can't clearly figure a reason. Temperature could play a role but it seems yours is relatively constant.

Maybe some increases in the overall concentrations of calcium and carbonate are occurring from evaporation,ie less water to hold it in solution to a point where some precipitation of insoluble calxium carbonate occurs. Then if fresh water is topped off later it will result in a weaker concentration than the original one.
The dripping condensation from the lid is from evaporation; correct? If so it shouldn't cause a drop but rather help to keep the salinity constant.

[AquamanE]

JGoal- Very interesting question- Im sure the gurus in this chemistry forum will have an answer for you. If these guys cant, i dont know who could.

[Crackem]

Jorge what are you using to test alk and ca? How old are your reagents? If using Hanna for alk, have you changed batteries lately?

[Jgoal55]

The dripping condensation from the lid is from evaporation; correct? If so it shouldn't cause a drop but rather help to keep the salinity constant.

Yes, the dripping condensation is from evaporated water. I guess you're right in that it would do nothing more than help keep the salinity stable (which it is very stable because before I stared testing this container the one thing I always did check before a WC was my salinity and temp).

Jorge what are you using to test alk and ca? How old are your reagents? If using Hanna for alk, have you changed batteries lately?

Yes, actually changed batteries a few days ago in Hanna and also have double checked results a few times with Salifert. For the calcium, I only have Salifert but ime, it's always been very accurate.

JGoal- Very interesting question- Im sure the gurus in this chemistry forum will have an answer for you. If these guys cant, i dont know who could.

lol. me either.

[dkeller_nc]

I would consider this completely normal, especially over a two month period. In fact, I observe a similar alkalinity drop over a week's time with Instant Ocean. Because I want the alkalinity to drop, I consider this an advantage (although I help it along with a tablespoon of calcium chloride in about 25 gallons).

[Jgoal55]

over two months sure, but you would consider it normal over the time period tested? thx.

[dkeller_nc]

Yes, of course. In my hands, IO mixes up to about 10 dKH (testing about 7-8 hours after mixing), it's at about 8 dKH after 2-3 days, at 75 deg F and circulating, even without any CaCl additions. That's accompanied by a fair bit of precipitation on the walls of the container (though not enough to be concerned about).

[Jgoal55]

Interesting thanks. Part of the issue is that with such a small tank I sometimes go overboard on the amount of water changed so if my new SW isn't at the right parameters, and I change to much, it could affect the display readings. I never worried too much about it but it's something I'll keep in mind going forward. I guess with a nano in particular it's more important to do frequent small changes (maybe weekly or bi weekly), than large monthly changes.

[dkeller_nc]

I guess with a nano in particular it's more important to do frequent small changes (maybe weekly or bi weekly), than large monthly changes.

This is one reason that I count on the alkalinity decrease after a few days mixing/storage of IO. I also have small tanks, and I definitely don't want to do a 30% change with seawater that's in the 10-12 dKH range (I'd much rather dose).

[tmz]

I like small changes for a variety of reasons regarding consistency regardless of the size of the system. FWIW, I change 1% dailly with an occasional 5% change during maintenance. It's easier for me to do it that way.

[AquamanE]

Yes, of course. In my hands, IO mixes up to about 10 dKH (testing about 7-8 hours after mixing), it's at about 8 dKH after 2-3 days, at 75 deg F and circulating, even without any CaCl additions. That's accompanied by a fair bit of precipitation on the walls of the container (though not enough to be concerned about).

Thats a very interesting observation. and all though ive never checked other than the original batch im glad it drops. One of my biggest issues with IO has always been the high ALK so ive avoided it. However its been really hard for me to not buy it recently since DD salt has been difficult to come by locally, and IO salts have been at really good prices lately even delivered.

I wonder if this happens with all salts or just IO.

[dkeller_nc]

I would imagine that all artificial salt water mixes would do this over time (drop in alkalinity) presuming that they start out high (>9 dKH) and the manufacturer hasn't specifically added organics or other compounds in an attempt to stabilize precipitation.

Regarding using IO, though, lots of very successful reefers use IO and simply adjust the calcium, alkalinity and/or magnesium to their liking. It certainly doesn't seem to cause any issues in and of itself versus more expensive sea salt mixes.

[billsreef]

FYI, the alk is reacting with the CO2 in the air over time ;)

[dkeller_nc]

FYI, the alk is reacting with the CO2 in the air over time ;)

Well, it's theoretically possible to lose a very small part of the total alkalinity via CO2 off-gassing, but I'm pretty sure most of the alkalinity drop with IO is just calcium carbonate precipitation. That's OK by me, b/c calcium chloride is dirt cheap.

But it does make me wonder why they formulate it with so much carbonate/bicarbonate in the first place.

[Jgoal55]

Especially if the container is outdoors I'm guessing C02 would be even less of a factor right?

But yes, I have recently switched to smaller WCs and things are better.