Alkalinity fluctuation question

[delphinus]

Yet another alkalinity question .....

Does alkalinity fluctuate over a 24-hour period, having a peak high and a peak low? Or is it steady (barring for any demands on it that slowly pull it down over time)?

You know how pH fluctuates between day and night. For example, of late, if I test my pH in the evening just before lights out, my pH reads 8.4. If test my pH in the morning just before lights on, my pH reads 8.1. Does alkalinity do something similar?

I've been testing to watch my alkalinity daily to see what sort of draw it has on it. However I was on a course last night so I was unable to test my water until well after lights out (got home around midnight -- tank lights go out at 9pm). What I found surprised me: whereas I had tested a level at 2.8mEq/L the day before (but had done that test about 6pm, so well before tank lights out), I now read a level at 2.1mEq/L. If a daily fluctuation doesn't account for this, then I'm looking at a 0.7mEq/L (almost 2 dKH) drop in a 24 hour period and that kind of makes me nervous that the system is completely off-balance. Should I panic?

[Randy Holmes-Farley]

Delphinus:

A heavily stocked tank can easily drop 1 meq/L/day of alkalinity, so there is no need to panic.

The alkalinity does not follow the pH day/night swing. That change is largely due to changes in CO2, and CO2 cannot have any change on total alkalinity.

It is an interesting question of whether alkalinity declines more during the day or during the night. It will depend upon when the most calcification takes place. The only paper that I've seen said it happened more at night, but recent discussion of this topic online seemed to suggest that the final answer wasn't in yet.

[delphinus]

Thanks, Randy.

I do have a fairly serious SPS load in this tank (mostly frags, but a few moderate sized acropora colonies). The corals look fine but have slow growth compared to other people's tank (N03, PO4 levels are nicely very low in this tank, touch wood.)

It's been recommended to me to use Seachem Reef Builder to raise my Alk to NSW (or slightly above as some seem to recommend).

The recommended dosage as indicated on the bottle seems to raise Alk by about 0.2mEq/L (per dosage). I assume I should not be going above the recommended dosage, but how would I go about raising the Alk if I have that strong a drop in a 24 hour period? I assume I wouldn't want to add more than the recommended dosage in a given 24-hour period on account that I might be stressing the animals otherwise. Or would I? Do I start at the recommended dosage, and then "up it" or "back it off" as required to get the number to start drifting up and then taper off as it gets to NSW or slightly above?

Any advice?

[Randy Holmes-Farley]

Delphinus:

<< Do I start at the recommended dosage, and then "up it" or "back it off" as required to get the number to start drifting up and then taper off as it gets to NSW or slightly above? >>

That's the ticket:)

Take all manufacturers recommendations with a grain of salt. If you have accurately measured alkalinity, there's no reason to not add enough of a normal alkalinity booster to maintain the tank at the desired level.

0.2 meq/L/day is not enough for most tanks. Are you sure that's what the max dose works out to?

[andy-hipkiss]

Randy,

Strange this should crop up ... I am monitoring my alk levels today trying to detect such a change. At lights out +30 mins, my alk has dropped .1 meq/l from the value at lights on +2hrs ... I'll continue taking tests to see.

However so far it appears that the CaC03 demand is almost level 24/7. I'll repost if in the AM, (lights on -3 hrs) if there is anything significant to report.

Maybe I need to run a higher resolution on the alk test??????

[Randy Holmes-Farley]

Andy:


Thanks, Andy! I'll be real interested to see the alkalinity drop in the opposite period. Needless to say, you didn't add anything in between measurements, like limewater on automatic, did you?

<< However so far it appears that the CaC03 demand is almost level 24/7>>

That means the calcium demand?

The way that i came up with a value for the alkalinity demand was pretty simple, and I hope it reflects actual values.

I figured that a heavily loaded tank would take 2% evaporation replacement daily of saturated limewater. The alkalinity of the limewater is about 41 meq/L. So the tank water is being boosted by about 0.8 meq/L each day in that situation.

[andy-hipkiss]

Randy,

The Ca reactor is on constantly and driven by a peristaltic pump so +/- it provides a constant input. My solenoid is set so low that the CO2 never gets turned off.

I'll let you know in the AM if I can detect any change. I once calculated that my tank draws 12.something kg/m2/yr so I hope that on standard resolution the Salifert can detect the changes. At the moment if I don't run the reactor I lose well over 1meq/l/day (I think the CaCO3 demand has increased since I last calculated it).

Is there anything in particular you'd like me to measure?

rgds

[Randy Holmes-Farley]

Andy:

It's complicated with the reactor running. With it constantly adding alkalinity, the alkalinity will possibly drop during high calcificaton times and rise during low times.

Consequently, it would be interesting to see what happens in the opposite time period from what you measured, but i'd expect the effect to be small.

[delphinus]

Originally posted by Randy Holmes-Farley

0.2 meq/L/day is not enough for most tanks. Are you sure that's what the max dose works out to?

Actually I guess that's the thing, I don't know what the "max" should be or even how often I should be adding it.

The SPS in the tank don't seem to mind, but the carpet anemone absolutely hates the reef builder. In 18+ months that I've had her, she has never reacted so negatively to anything as much as she has been doing this week since I started the additions; she completely buries herself into the sand and disappears for a few hours after each addition. But then the way I've been adding the powder is by putting in the dosage all at once, one time per day. Conceded, it would be better to put the reef builder in a topoff reservoir (I just haven't built a reservoir for the tank yet ... but it could be done.) Failing that, i.e., the anemone still looks unhappy while having the reef builder being added, then I guess I would have to discontinue the reef builder, and resign to that I will never have substantial SPS growth in this tank. It's a 20 gallon so I'm not so sure that a Ca Rx would be an economically sound venture... on a bigger system there'd be no question.

Another lesson in why it is never good to try to accomplish too much in one tank, I guess... :(

[Randy Holmes-Farley]

Tony:

<< But then the way I've been adding the powder is by putting in the dosage all at once, one time per day. >>

Powder directly to the tank? If so, that might be the problem: some solids may hit it. Try dissolving it in some Di water first.

I can't recall exactly what is in reef builder, but you might try simple baking soda for a few days and see what the anemone thinks.

There are lots of ways to add alkalinity that shouldn't cause a problem for an anemone. The two part systems are a good choice for a small tank (B-ionic, C-balance, Kent's equivalent, etc.).

[andy-hipkiss]

Randy,

I'm not sure how much the reactor complicates things. Sure when alk demand by the corals increases leading to a lowered alk in the water column, the reactor can more readily dissolve its media but I wonder how significant the effect truly is? Does, say, a 0.1 meq/l change in water column really change the dissolution rate?

Anyway summary so far (figures approx (i.e. guessed if between the graduations on the 1ml syringe of the Salifert kit))

08:00 VHO actinics on
10:30 MHs On
13:00 3.40
17:00 3.35
20:00 MHs off
21:00 VHO actincs off
20:30 3.30
00:30 3.30
08:00 VHO actinics on
08:30 3.30
10:30 MHs on
11:00 3.50
13:00 3.40

I suppose I need to look more closely at the lights off period, but it appears that CaCO3 usage is pretty constant apart from around the period when the lights come on.

[Randy Holmes-Farley]

Andy:

<< I'm not sure how much the reactor complicates things. >>

I wasn't even thinking of changes in the reactor output based on tank water changes, but a more simple issue:

I agree that one can sort through it easily enough, but having the reactor on makes the alkalinity rise during a time of less alk consumption. If you want to know what percentage is depleted in each time period, you have to know how fast the alkalinity is being added by the reactor (or equally, how fast it is depleted when the reactor is off).

If the reactor were off, you could just compare the drops and see which one was bigger, and by what percentage.

As it is, you don't see much change, so the point is rather moot.

<< I suppose I need to look more closely at the lights off period, but it appears that CaCO3 usage is pretty constant apart from around the period when the lights come on.>>

I agree, it looks very steady. That's a nice experiment and I appreciate hearing about it. I've never seen data like this before. :)

[andy-hipkiss]

Randy,

I'll do the test again next weekend, as looking at the figures, it appears I get a slight increase in Ca/alk demand within the last hour or so of MH's off ... perhaps extending the light period another hour might be of benefit.

Regarding turning the Ca reactor off, I'm not sure ..... it seems that your assumption is that coral growth rate is not affected by Ca/alk levels .... now let's say in the range 3-3.5meq/l, things are level, but comparing 3.5 vs 1.7meq/l ... hmmm dunno, I would GUESS that a slow down could be observed.

The purpose of my test was to start to explore the claim that a Ca reactor should only be run during the period of highest pH (i.e. light hours). I'm not convinced ;)

[Randy Holmes-Farley]

Andy:

<< The purpose of my test was to start to explore the claim that a Ca reactor should only be run during the period of highest pH (i.e. light hours). I'm not convinced >>

I've not heard that before, but based on your alkalinity data, it doesn't seem like an especially good idea. I guess the question is how much the alk would drop if it were off for a few hours, and whether there is any benefit to doing so (which I presume is a higher pH, or at least a lower minimum value).

<< .... now let's say in the range 3-3.5meq/l, things are level, but comparing 3.5 vs 1.7meq/l ... hmmm dunno, I would GUESS that a slow down could be observed. >>

Good point. That's probably a bigger complication and to be avoided if you are trying to understand rates during the day and night.

[andy-hipkiss]

There's some "interesting" concepts coming out of Germany at the moment.

Some seem to be using a sledgehammer to crack a walnut (and then needing another sledgehammer to fix a subsequent problem etc).

However, there's no denying that that are some great tanks in Germany so these techniques are worth looking at.

One I'm not going to bother trying is running a kalk reactor but with saltwater in the same way a Ca reactor recirculates tank water. I really can't see any benefit of doing so ... any ideas???

[Randy Holmes-Farley]

Andy:

<< One I'm not going to bother trying is running a kalk reactor but with saltwater in the same way a Ca reactor recirculates tank water. I really can't see any benefit of doing so ... any ideas???>>

It sounds tricky to run seawater over Ca(OH)2 and get some of the Ca(OH)2 to dissolve, but not so much that the pH rises and causes precipitation of CaCO3. Without seeing one in operation, I'd be pretty skeptical. Is there any CO2 involved?

[simonh]

I also saw Craig Bingman mention on RAMR that adding calcium hydroxide directly into seawater was not a good idea. It would precipitate the magnesium hydroxide and is commercially used for this purpose of extracting magnesium hydroxide from saltwater. He did say that the magnesium hydroxide should re-dissolve back at normal pH values. However in a stirrer I would imagine the high pH would mean that the magnesium hydroxide precipitates and wouldn't have chance to re-dissolve?

[Randy Holmes-Farley]

Simon:

<< However in a stirrer I would imagine the high pH would mean that the magnesium hydroxide precipitates and wouldn't have chance to re-dissolve?>>

Another good point. We can see such precipitation that redissolves when we add limewater or things like B-ionic to tank water, but if the stirrer were perpetually high in pH, Mg(OH)2 might pile up on the bottom, along with CaCO3.

[Randy Holmes-Farley]

Andy et al:

Here's a reference tha I came across today on this topic:

Carbonate production of some calcifying algae in a French Polynesia coral reef. Payri, Claude Elisabeth. Lab. Ecologie Marine, Univ. Francaise du Pacifique, Tahiti, Fr. Polynesia. Bull. Soc. Geol. Fr. (1995), 166(1), 77-84.

Abstract:

On the northwestern part of Moorea Island, calcification rates for 8 benthic species (Halimeda opuntia var hederacea, H. opuntia var. opuntia, H. incrassata f. ovata, H. discoidea, Amphiroa fragilissima, Porolithon onkodes, Hydrolithon reinboldii and Padina tenuis) were estd. using the total alky. method during 24-h-cycles, spread over the course of a year. The daily calcification rates vary significantly among the taxa. Halimeda play a major role in the carbonate budget and particular in the sediment deposition. The hourly rates vary over a 24-h-cycle with a decrease during the night period. Moreover, the calcification measurements spread over the course of the year exhibit a strong seasonality in the carbonate prodn. Lastly, the annual inorg. carbon budget shows that these species play an essential role in the balance of the reef calcification rates.

[andy-hipkiss]

Randy,

Interesting. I guess that what we can conclude is that all tanks will be different. Mine is almost entirely SPS with no calcifying algae beyond some coralline algae.

If it weren't for my dislike of relying on a solenoid and timer turning CO2 on and off, I can certainly see the point of controlling a Ca reactor in this way depending upon the aquarium's inhabitants.