Alkalinity Question

[broomer5]

55 gallon FOwLR / some inverts.
Approx. 35-40 lbs LR
Crushed coral / aragonite substrate 3-4"
Most water parameters good/stable.
pH between 8.1 and 8.3
Ammonia 0
Nitrites 0
Nitrates < 10
Phosphates about .2 - .4ppm
Calcium once at 375ppm but 255-300 more common.
SG 1.22 - 1.23
Tank has been set up for about 4 months.
Some small spots coraline appearing on glass.
Instant Ocean - 10% changes every 3 weeks.
Use RO for makeup, top-offs and changes.
Carbon in wet/dry filter occasionally.
Water turned over approx. 7-8 times/hour sump/wet/dry
Powerheads - 2
Protein skimmer working well - runs continuously.
Lighting - crappy 40 watt single 48" 50/50.
Supplements: Kent Marine Superbuffer dKH as required to maintain pH.
Seachem Reef Calcium as directed on bottle.
CombiSan by Two Little Fishes as directed.
2" Maroon Clown, 1" Percula, 6 damn-sels, 1 coral-banded shrimp, half doz. Turbos and doz bluelegs.
My question: I am working to get water quality stable and within levels for future corals. Then new PC lighting. Excess fish will be removed well before that time.
My alkalinity is SKY-HIGH at 18-21 dKH or around 6.5 to 7 meq/l
Calcium levels hard to maintain.
Appears that calcium has precipitated out onto rock as whitish particles ( happened once 3 weeks ago ).
How is it that my alk is so high, and how would I lower it. Seems to be various opinions and levels as well.
Any ideas ???
Thanks, Broomer

 

[kris]

18-20 is very high, I was told to keep it under 15 with 10-12 being optimal. Your superbuffer dkh is what's driving it up. you shouldn't need it with your r/o water. If you are using this to raise or maintain ph try seachems "marine buffer" which does the ph trick without increasing dkh.
If after a few water changes it has not dropped write back.
Good Luck

 

[mako]

High alkalinity can also be caused by a low carbon dioxide exchange and will ionize the water forming a carbonic acid thus lowering the P.H.
Try to increse the water movement at the surface by aiming a powerhead so that it breaks the water but not create a splash this should help lower the alkalinity and stabilize the P.H.
the more animals in the tank and the more food used require more aeration.

 

[broomer5]

Thanks Kris & Mako !
Both of your replys sound like good advise. Did a 10% H2O change today, no buffer additive. Redirected a powerhead at one end of tank and the return nozzle from sump at other end of tank, both pointed up towards the water surface.
Lots of surface ripples and agitation now.
I'll wait a few days and test again.
Brian