Alk Fluctuations

cope413 · Dec 24, 2014

I recently started auto dosing with BRS 2 part.

I have a 40B/20g sump that's about 1 year old. I had previously been managing alk with baking soda in my top off water. Cal was replenished easily enough by WC.

Coral load increased and couldn't keep that up, so started dosing about 1 month ago.

I use IO, and I dose ~20ml of vinegar/day

I'm currently at 16.5ml/day of 2 part. The calcium is dosed 1 hour after lights on (over 15 minutes with BRS doser).

My pH had been pretty steady - 8.0 - 8.15 - but figured I'd try to make it even more stable, so I dose alk 2, 4, and 6 hours after lights out. 5min each time.

So here's my question

My alk reads as high as 9.6 and as low as 8.0. The average is probably 8.4.

Is this normal? Is this ok?

It's been 1 month since I started dosing, and I initially started at 22ml/day and came down to where I'm at now.

Cal has leveled off around 440-450, but I really have no idea on any given day what my alk will read.

My tank hasn't looked better, and I test at the same time every day (approximately 30 minutes after lights on). From what I've read, this seems to be odd. It's also outside of what I should expect from test tolerance/variance. I use Red Sea test kit.

I'm definitely not a parameter chaser. The only reason I'm asking is because stability is paramount for me and this seems, based purely on a numbers/statistical level, to be an instability.

Not sure if it's relevant, but here are other numbers

Salinity - 35ppt
Phosphates - 0 (hanna)
Nitrates - 0 (elos)

Lighting schedule
Blues 11 hours. Whites 9 hours.

Last alk dose is ~6 hours before lights on.
It's dosed right above a powerhead in my sump.

Thanks in advance for help/insight

Merry Christmas!

NanaReefer · Dec 24, 2014

Following! Same exact setup/same 2part dosing/same ALK fluctuations. Different dosing regimen. I'm up to 17ml a day of each, broken up 8.5ml 2x daily.

Randy Holmes-Farley · Dec 24, 2014

It is probably OK, but why not spread out the alk dosing more to smooth it out?

cope413 · Dec 24, 2014

I can, and plan to, but I wanted to get the dose right before doing that. Also,my pH is stays within 8.0-8.15, so it seems pretty smooth on the pH side.

Would spacing it out affect the alk readings?

Randy Holmes-Farley · Dec 25, 2014

When you measure in relation to when you last dosed will impact readings.

cope413 · Dec 29, 2014

So I changed my dosing to dose 1ml/ hour for the first 4 hours after lights out. Then 2ml/hour for the next 4 hours (when pH is lowest), then 1ml for the last 4 hours before lights on. The only change I've noticed is pH is slightly higher before lights on 8.04 vs 8.01

Still getting the range between about 8 and 9.6 in alk

Randy Holmes-Farley · Dec 29, 2014

That sounds good, but dosing during the day as well will stabilize it more, if you want.

cope413 · Dec 29, 2014

Ok. Which is more important, alk stability or pH stability?

I know there's some sort of equilibrium with them, but it seems like if I dose during the day, the difference between my peak and low pH will be bigger than dosing only at night.

Or does it matter? If there isn't any real issue with that flux in alk, then I'm inclined to let it be as my tank is very happy atm. I really just wanted to know if there are any potential issues with that sort of change, or if it indicates something else isn't right.

Randy Holmes-Farley · Dec 29, 2014

Alk stability is likely more important, both by experience folks have and by the fact that it doesn't change in the ocean, while pH does.

But if it is not an SPS system, especially a ULNS SPS system, it may not matter that much.

cope413 · Dec 29, 2014

Great to know. I will spread out the alk evenly throughout the whole day and see what happens. How big of a pH spread is acceptable?

Randy Holmes-Farley · Dec 30, 2014

The daily pH swing is not, IMO, a concern. It is the extremes that are the concern. If the pH stays above 7.8 and below 8.6, I wouldn't worry much about it.

That said, more aeration will smooth it out.

NanaReefer · Dec 31, 2014

Randy-Is there a best time to test for ALK/Ca/Mag? Does it really matter when? Is there truth to best time being before lights on?

Randy Holmes-Farley · Dec 31, 2014

It doesn't matter at all what time of day you test for those, but it does matter, obviously, whether it is right before or right after dosing.

NanaReefer · Dec 31, 2014

Ok. So I'm testing right before a.m. dose and 10-12hrs after night dose. Will the a.m. number be the correct number or no? Every morning I'm getting 8.4 after having dosed 10ml 10-12hrs before.

Randy Holmes-Farley · Dec 31, 2014

The 84 is alkalinity in dKH? Then the tank likely boosts to a higher value then drifts down until the PM dose, then spikes up on dosing and drifts down until the PM dose. The tank is seeing a range from the value just before dosing to the value you get once the dose is mixed in.

Those numbers seem fine to me.

NanaReefer · Dec 31, 2014

Yes that is dkh. I thought ALK swings were bad? If it raises during the day from dosing but falls throughout the night, isn't this a bad thing?

Randy Holmes-Farley · Dec 31, 2014

I do not know if regular, daily fluctuations are bad. The concern and the anecdotal data seems to be with alk going up or down significantly over longer time periods. That way a coral would adapt to a lower or higher level, then be placed into something it wasn't accustomed to. With regular daily variations, it is adapted to the average of those, and doesn't constantly change its biochemistry (things like number of bicarbonate transporters) to adapt to the moving value of alkalinity.

That said, you'rs isn't going up and down that much if you are dosing twice a day.