Declining Alkalinity

CastAway · Jun 23, 2015

In general, my Alk and pH seem to be declining over time. Three months ago for example, my dKH would average 9 and my pH 8.3. Now, my pH is 7.9 and dKH 7.6.

I always attributed my higher dKH to my Ca reactor, and to lower my dKH I used to tune down the effluent output. This worked pretty effectively.

These days however, my Ca reactor effluent output is higher than ever, and I have what I would consider a borderline problem with low dKH/pH. It seems like it's on the threshold, anyway.

Could it be that the house is closed up, and the AC is on?
Is the low pH simply a symptom of the low dKH?
I have had some increased alk consumption, I'm sure, but can all of the decline be attributed to consumption in coral building?

Ca consistent at 430. Mg consistent at 1350, manually dosing Ions.

Randy Holmes-Farley · Jun 23, 2015

The difference in pH you see is much more than that small difference in alkalinity will cause. Alk would have to drop by more than a factor of two to explain a 0.4 pH unit drop in pH.

A closed house and increased CO2 from the reactor both can contribute to lower tank pH.

The decline in alk very likely is from increased demand not being quite maintained by the reactor. I'd suggest tweaking it more if you want the alk higher. Adding more CO2 may help, although without knowing details (like the effluent alkalinity), it is hard to say from afar.

CastAway · Jun 23, 2015

Hoping to effect some change to the situation, I just refilled my Ca reactor with fresh media. I use CaribSea ARM - Fine. Therefore, I just re-calibrated by pH probe, and the rector is currently running at 6.8. Although I have measured output quantities, it's difficult as the rate changes as the feed tube/roller clamp clogs.

Is this a time where I might consider dosing limewater Randy, to raise the pH? Will this also raise the dKH?

Randy Holmes-Farley · Jun 23, 2015

CastAway said:
Is this a time where I might consider dosing limewater Randy, to raise the pH? Will this also raise the dKH?

Yes and yes, but at pH 7.9, I wouldn't say it was a nice to have, not a need to have. As it raises pH, it also raises demand, so the effect on alk is difficult to determine in advance.

How long has the reactor had the new media?

CastAway · Jun 23, 2015

Twenty four hours now, with the new media.
Reactor pH 6.8

Tank:
pH 7.9
dKH 7.6
Ca 430
Mg 1360

Perhaps a 0.3 increase in dKH in the last 24hrs.

Randy Holmes-Farley · Jun 23, 2015

I'd let it go another day or two before making any changes. You may end up having to raise the pH in the reactor.

CastAway · Jun 23, 2015

Thanks Randy!

I'll keep watching.

Randy Holmes-Farley · Jun 23, 2015

You're welcome.

Let us know what happens!

CastAway · Jun 25, 2015

So, I have not done a thing since my last post here – same CO2 input to reactor, same effluent output rate, although the pH in the reactor is now 6.6, just a bit lower than it was.
The tank pH is now 8.1, and the dKH remains 7.6. Calcium remains 430.

This all seems strange to me. With a lower Ca reactor pH I would expect a lower tank pH. But, perhaps the system is successfully off-gassing the CO2.
With a rising tank pH I would expect a rising dKH. But I think this is the change in demand you said would make it hard to determine.
My instinct is to buy some Salifert tests to make comparisons to my Red Sea kits, and, to continue watching and waiting for stable measurements. Then, perhaps an increased effluent output will raise tank dKH/Ca while lowering the reactor pH.
Randy?

hart24601 · Jun 25, 2015

Have you been noting the days that the AC is on vs off and if you have windows open even at night? The furnace in winter makes a small difference with my tank, but the AC in summer is crazy. I just note the general pH trend and when we fired up the AC I saw a huge drop in pH and was worried some dosing was off before I noticed the cause was the AC.

Apex values from this week. It was cool and windows open = 8.33 consistent daytime high pH reading. Night drop was to 8.1. It got hot and we closed up the house and the max is only 8.06 and night low is 7.9. It has been repeating with those values consistently when the house is open, or even just without the AC on, vs running the AC. I dose kalk along with 2 part.

Randy Holmes-Farley · Jun 25, 2015

Lower reactor pH does not always translate to lower tank pH. Flow through the reactor is a big part too, as, of course, is the amount of CO2 in your home air.

I wouldn't spend time thinking about the tank pH since it is well within norms, and focus on keeping the alkalinity where you want it.

CastAway · Jun 25, 2015

If the reactor supplies Ca and alk in balance and proportion to one another, and my Ca is at an acceptable level but the alk is not, is it reasonable that I might have to supplement by dosing alk?

I just never imagined I'd have to supplement alk or Ca while using a Ca reactor.

Perhaps I should add, I did upgrade my lighting a couple weeks ago, and think I am experience some accelerated growth. If so, does coral growth result in depletion of alk and Ca in proportion to one another?

Randy Holmes-Farley · Jun 25, 2015

CastAway said:
If the reactor supplies Ca and alk in balance and proportion to one another, and my Ca is at an acceptable level but the alk is not, is it reasonable that I might have to supplement by dosing alk?

No necessarily. Not sure what your numbers are, but if you boost the reactor to raise the tank alkalinity by a full 3 dKH, calcium will only rise by about 20 ppm, and will still be fine.

CastAway · Jun 26, 2015

Okay, I think I'm back where I want to be, better than I was, at least.

Current tank params:
pH - 8.1
dKH - 8
Ca - 445
My - 1380

I increased the Ca reactor output rate to 75mL per min. (not sure what it used to be)

Effluent params:
pH - 6.75
dKH - 12.6
Ca - 485

No change in 48 hours now.

The new LED's have a much improved spectrum, and I now attribute this alk decline to simple increase in demand. I'm seeing some accelerated coral growth. The lower pH I'm attributing to exhausted Ca reactor media.

Sound reasonable Randy?
Are my numbers anomalous?