Reason for unstable ALK?

NanaReefer · Sep 11, 2014

40B/20L sump. My Alk has been running on the lower end of what's acceptable since the beginning of my tank. Now into it's 15th week running.
7.6 seems to be the norm. Never higher without dosing. If I don't dose 6.7 being the lowest so far.
Been dosing 20ml of BRS 2 part Alk only to maintain the 7.6 missed a couple days and it dropped to the 6.7. Dosed 20ml again and 2 days later it's back up to 7.6. But I want it a little higher, around 8.4 so I dosed 30ml yesterday morning and by early evening it was at 8.4 which scared me because I didn't think it would jump that fast. Tested this morning and it's back down to 7.6.
Ok I'm not liking this swinging.
Please what is causing these Alk swings?
Great flow, great surface flow.
Tank is LPS dominant, 1 SPS. 12 total. 2 fish. 10g WC Bi-weekly.
Ca has been very steady at 450 (no dosing)
Mag has been very steady at 1440 ( no dosing)

Randy Holmes-Farley · Sep 11, 2014

The alkalinity that is used depends on the alk value.
Not much is used at 6.7 dKh and so it drops until that point and slows way down.
When you dose, the alk rises and the demand is higher at 8.4, and so it begins to drop again after dosing.

This is all normal and you should anticipate dosing every day, maybe several times per day.

NanaReefer · Sep 11, 2014

Thank you Randy!

JOKER · Sep 11, 2014

Dosing pump is your friend. Keeps parameters way more stable and with controller you can dial them to whatever level you want and dose small amounts throughout the day.

rayn · Sep 11, 2014

I have been having the same issue, this makes sense. Dosing pumps seen to be the way to go here for sure. Thanks Nanareefer for bringing this up.

Velodog2 · Sep 11, 2014

Will Alk usage rates vary by time of day as well?

Randy Holmes-Farley · Sep 11, 2014

Velodog2 said:
Will Alk usage rates vary by time of day as well?

Maybe a little (usually more during the day), but spreading the dosing out over the whole 24h equally (with a timer, for example) is fine if you have a pump.

If not, I'd suggest dosing when pH is lowest, in the late night to early AM.