Alkalinity chemistry off?

[Reefer PT]

I'm just in the process of setting up a dosing system on my 93gal reef using peristaltic pumps controlled by my APEX. So every day I've been testing to try and "dial it in" One thing I have noticed is that the Calcium uptake is a steady 15ppm/day but the alkalinity is all over the map. I'm up to 6.8 dkh per night (which is 200ml of Redsea reef foundation b stock solution) and still manually adding anywhere from 1.7-6.0 dkh worth of solution to try and reach a dkh of 12. every day I'm adding 25ml to the dosing program to try and reach equilibrium.
This just seems off to me. Why would I be using so much buffer? Is this just a symptom of a bigger problem? Is it the buffer I'm using? I used to dose weekly by hand. My tank would always test out at about 8.6dkh and I would add 34 ml of the liquid form of reef foundation b and be done with it. I know the stock solution is about a third of the concentration of the liquid form but I honestly thought I would use about 100ml per week. I didn't test every day so the dkh must have shot up to 12 when I dosed then just dropped very quickly again without me knowing. My tank must like being at 8.6dkh.
Other parameters: PH 7.8-8.2 (daily swing per apex), Ca 460ppm, mg 1400, temp 78.5-79 deg, NO3 1ppm, PO4 .04ppm dosing 6ml/day of NOPOX (been doing so since January)

1. Is this Normal or should I be concerned about adding too much buffer?
2. is a 12dkh an unreasonable goal?
3 Should I be using pure sodium carbonate instead of the red sea product?

Thanks in advance
Dave

 

[disc1]

1. that sounds like too much buffer
2. 12dKH is awfully high. 8 or 9 might be a more reasonable number. With your calcium on the high side I bet half or more of the two part you're dosing is just turning to sand.
3. If you're running things that high and pushing calcium carbonate precipitation I'd be dosing the un-baked baking soda to try to keep pH down.

 

[Reefer PT]

I was going off the RedSea recommendations:
Optimal levels of salinity, KH, Ca & Mg according to type of aquarium:

Aquarium Type Salinity (ppt) Alkalinity (dkh/meq/L) Ca (mg/L) Mg (mg/L)

SPS Corals,Frags/Calms 35 12.6 / 4.5 465 1390

So this is not a natural or reasonable goal to obtain. I guess I was hoping for accelerated growth by following this program. Guess all I am doing is throwing money away on product.

What would you say a "good" amount of buffer would be? I know its the dkh number I'm shooting for but if I'm adding 200ml to maintain say a 10dkh would that still be too much?
Dave

 

[disc1]

I don't know what a good amount of buffer would be. 200ml doesn't sound way too high. It all depends on the alk number.

A few years ago lots of people were recommending really high alkalinity values for some reason. In more recent times that recommendation has changes. Lots of people started running low nutrient systems and noticed that SPS corals burned when the alk was way above natural levels. So lots of folks started running with alk at levels just above natural levels, so 8 or 9dKH.

I don't personally keep SPS so I can't really make that recommendation one way or another, I can just tell you what I've noticed the people that do keep SPS doing.

 

[Jimmy54]

According the 15 mg/l calcium uptake - the dkh drop should be somewhere around 2.2 (approx 1 dkh for every 7.1 mg/l calcium)
For a 93 gallon or 352 l tank you should dose approx 3.5*22 = 77.5 ml (the label says 1 ml / 100 l / 0.1 dkh)

What I would do is stop dosing both calcium and RF-B till they're back on "normal levels" like 8/9 dkh and 430/440 for calcium.
Then figure out how much calcium the corals really take up and start dosing accordingly.

I think David is right - you're creating sand when you're dosing 200 ml RF-B.

 

[Reefer PT]

Just to clarify, I'm dosing the stock solution made from RF-b powder which instead of .1 dkh/ 100l has a concentration of .034dkh/100l. Or about 1/3 strength. So then about 230 ml based on calcium uptake? Will shut down dosing for now and let it fall a bit. Thanks for the advise.
Dave