new to dosing test question

[MBX5]

So I've been searching all over and can't get a definitive answer on when to test. I just started using the BRS 1.1ml dosing pumps with BRS 2 part. What is the best time to test alk and ca? I tested tonight just before the pumps started and my alk is at 7.2 way too low as I'd like to keep it around 9 my ca is at 415. I've been dosing 15ml the last three nights and the pumps run from 11pm to 10am. Should I test during the day or just before the pumps start pumping? One other question is should I dose to bring it up first or just bump up the amount my pumps are dosing? Thanks guys I'm real green to all this dosing stuff.

 

[Newb73]

Doesn't matter. The key is to test at the SAME TIME every day (assuming you are keeping the same schedule).

Okay so lets say you test in the am...you might get consistently higher results (depending on how much alk your tank consumes in a day). So if you test at 8am you might get 8.2 and if you test just before bedtime you might get 7.5. The key is to set a goal and test at the same time every day. I usually test at night because I dose for the minimum, not the maxium.

High alk levels and nuking a tank scare me so I generally use the following: If dkh <8, increase by 5% to 10%. If dkh between 8 and 9 I do nothing (remember I test at night so my high point in the morning is likely a bit higher than the 9 am getting at night). If the DKH is higher than 9 I reduce the rate slightly.

I don't bother hand dosing I just turn it up around 5% and test again in a week. After a while you'll only test every couple of weeks and you'll get an even better idea of exactly what the pump should be set to. But don't do any water changes in between or that will screw it up. You want to test, wait a week (or two)...test again...make the appropriate adjustments THEN do your water change. You don't want your water change induced swing to be part of your adjustment.

Just for fun, you can test just after a water change to see what the swing is, but I would not factor that into my dosing formula. Over a period of weeks and month,s you will start to get a handle on it. After that the adjustments you have to make are less often and usually of a minor amount.

 

[Randy Holmes-Farley]

I agree that that reason you have not gotten a definitive answer is because it doesn't matter in most cases.

Of the things reefers test, only pH, ORP, and O2 change cyclically through 24 h (called a diurnal change). Timing of those measurements is important.

For calcium, alkalinity, magnesium, etc., those typically only decline between additions (or from water changes). Measuring just before an addition will tell you the lower limit, and a few minutes after (the time depending on how long it takes to mix in well) will give you the upper limit. Both bits of info can be useful.

 

[Newb73]

Ahh yes.

It is not a diurinal cycle. It is just dosing v usage.

I dose over night so it would peak in the morning and then the tank will consume some alk throughout the day so it would be lower at night just before i dose.

Its a user induced cycle, avoided if you dose on a 24 hr cycle, which i dont do because calcium goes in during the day and my ph already hits 8.3 when the lights are on.

 

[MBX5]

Thanks guys this helps. I guess I'm over thinking all this but I keep reading that we want the levels to be stable but not sure how I achieve that if I'm dosing only at night?

 

[Newb73]

Some people dose on a 24 hour schedule.

To eliminate the 2 part from forming a precipitate in a concentrated area you can dose to two different parts of the tank, for example have the alk fed to the return pump and dose calcium into rhe bottom of the overflow.

Personally what i would do is dose calcium at the top of the hour and alk at the bottom of the hour, leaving 10 of 15 minutes of time between where no dosing occurs.

As long as the ph doesn't swing above 8.4 AT MOST it is ok.

The way i do it i get a small alk swing but my ph is rock solid on a 24 hour cycle betweem 8.2 and 8.3.

I am not sure if its more important for the PH to be stable or to have the alk more stable on a 24 hour cycle.

Im gonna anxiously await Randy's response on that.

 

[MBX5]

So far my ph is 8.19- 8.27 so maybe I should do a 24hr dose? Once summer comes and the windows are open more I'm afraid it may jump higher.

 

[JimWelsh]

I agree that that reason you have not gotten a definitive answer is because it doesn't matter in most cases.

Of the things reefers test, only pH, ORP, and O2 change cyclically through 24 h (called a diurnal change). Timing of those measurements is important.

For calcium, alkalinity, magnesium, etc., those typically only decline between additions (or from water changes). Measuring just before an addition will tell you the lower limit, and a few minutes after (the time depending on how long it takes to mix in well) will give you the upper limit. Both bits of info can be useful.

I beg to differ. I tested Alkalinity on my display at regular intervals over the course of two-and-a-half days a few months ago, and graphed the results. There is a clear diurnal swing that is not insignificant, and, in fact, matches the hypothetical example that @Newb73 cited above quite nicely. My display was getting dosed appx. 100 mL per day of each part of RHF Recipe #1 in 1 mL increments spread evenly across the 24 hour period. Each data point is the average of three tests done in triplicate, with an uncertainty of <0.02 meq/L. Here is the chart of my diurnal Alkalinity swing:

 

[Randy Holmes-Farley]

I beg to differ. I tested Alkalinity on my display at regular intervals over the course of two-and-a-half days a few months ago, and graphed the results. There is a clear diurnal swing that is not insignificant, and, in fact, matches the hypothetical example that @Newb73 cited above quite nicely. My display was getting dosed appx. 100 mL per day of each part of RHF Recipe #1 in 1 mL increments spread evenly across the 24 hour period. Each data point is the average of three tests done in triplicate, with an uncertainty of <0.02 meq/L. Here is the chart of my diurnal Alkalinity swing:

We are debating semantics of what is a diurnal change, but you have a diurnal swing only because of how you dose alkalinity spread out, but not exactly matching the demand rate at every point in time.

The alkalinity only drops between doses, never rises(as you know) unless you are dosing more than the tank is using during some period.

So I agree that the consumption in the tank may show a diurnal change, but not the values between doses. :If you are dosing constantly (or nearly so) through much of the day, you may see swings in alk, just as one certainly would with once a day dosing.

 

[Newb73]

Is it possible that the uptake of alk occurs more during the day when the lights are on?

I had previously read that with SPS more encrustation occurs at night which would indicate to me that the levels would be more likely to drop at night.

...never a dull moment. To introduce biology to chemisty.....It Could just vary from tank to tank depending on the circadian cycle of the dominate species in a given set up.

 

[JimWelsh]

Is it possible that the uptake of alk occurs more during the day when the lights are on?

I had previously read that with SPS more encrustation occurs at night which would indicate to me that the levels would be more likely to drop at night.

...never a dull moment. To introduce biology to chemisty.....It Could just vary from tank to tank depending on the circadian cycle of the dominate species in a given set up.

In short, yes. The increased uptake appears to keep happening for a little while after "lights out" as well. Just look at my chart above -- it shows increased consumption between about 8:00 AM and 11:00 PM. Lights out on my tank is about 9:30 PM.

But, don't take my anecdote as meaning anything. You can read here a peer-reviewed paper that shows a very similar pattern (scroll down and click on the link to Figure 1).

 

[JimWelsh]

The alkalinity only drops between doses, never rises(as you know) unless you are dosing more than the tank is using during some period.

You made me go back and take another look at my data, and subtract out the amount of alkalinity I had been dosing, to see what the graph would look like. There are still increases, albeit smaller ones, between the hours of 11:00 PM and 8:00 AM. Continuing this game of "what if", I would have to subtract out twice the amount of alkalinity that I was actually dosing in order to avoid any parts of the graph where the slope was positive (meaning alkalinity was increasing).

Now, this tank is heavily fed, but also aggressively vodka dosed, and the nitrate level was in the 0.25-0.5 PPM range when this data was collected. I suspect that bacterial denitrification activity, perhaps itself a phenomenon with a diurnal cycle, may account for some of what I'm observing in the numbers.

Still, my point is that there is a measurable diurnal variation in alkalinity consumption, and it can be important to measure alkalinity at the same time each day, in order to be able to make a meaningful comparison of any two values. This is especially true if the purpose of the two measurements is to establish a consumption rate in order to regulate a dosing schedule.

 

[mcarroll]

You can read here a peer-reviewed paper that shows a very similar pattern

Good link - thanks!

Still, my point is that there is a measurable diurnal variation in alkalinity consumption

Seems to stand to reason given all we know about daily pH cycles, and how alkalinity and calcification are related to pH. I'd have been surprised if you said this WAS NOT the case.

 

[Randy Holmes-Farley]

Still, my point is that there is a measurable diurnal variation in alkalinity consumption, and it can be important to measure alkalinity at the same time each day, in order to be able to make a meaningful comparison of any two values. This is especially true if the purpose of the two measurements is to establish a consumption rate in order to regulate a dosing schedule.

I certainly do not disagree with the idea that it changes, and that one needs to pay close attention to when you are measuring with respect to dosing so you know whether it is a high point, low point, or something in between. I should have made that clear in my original post.

 

[MBX5]

So I did a water change and tested for 24hrs after just to see what was going on in the tank.
1. 10pm after the change and showed 8.3dhk
2. 9:30am 7.7dhk
3. 10pm 7.3dhk
Based on this I calculated off BRS adding 18ml from 10pm-11am with a total water volume of 18 gal will bring me up to 8.7dhk. I'm still confused on how to keep that stable during the day with that 1 DHK drop. Am I just over thinking it or is that 1dhk drop not a big deal?

 

[Randy Holmes-Farley]

IMO, 1 dKH is OK, but much bigger and you may want to begin dosing more often.

 

[MBX5]

IMO, 1 dKH is OK, but much bigger and you may want to begin dosing more often.

Guess I'll see what happens after dosing today and change if needed. Thanks

 

[Randy Holmes-Farley]

Guess I'll see what happens after dosing today and change if needed. Thanks

OK, let us know how things turn out.

 

[MBX5]

OK, let us know how things turn out.

Quick update
Alk @ 7:30am 8.6
Alk @ 3:30pm 8.4 Ca 425
Alk @ 9:54pm 8.4 Ca 425
So it looks like I may have a good dose? Now the question is my PH Average was 8.31 with a high 8.35 I know thats on the higher end but it seems like it's in range of what we want? Next I tested Mg @ 1500 I have never added any other than whats in water changes every week with IO. Is 1500 okay or do I need to try and lower that? I know in your article @Randy Holmes-Farley you say 1200-1400 ppm is acceptable but I've also seen 1500 is? Thanks again for all the help and info guys.

 

[Randy Holmes-Farley]

That pH is just fine. No other pH is "better".

The magnesium is fine too, but I would not add any.