Diagnosing Sudden Alkalinity - Is this normal?

[IronChefItaly]

Hello everyone, I've stumbled into yet another reefing obstacle and I think I know whats happening but I'd like to get some second opinions in case I'm heading for a crash.

My Current Parameters...(value in brackets is my target)
Salinity - 1.025 (1.025)
Temp - 77.0 (77)
pH - 8.05 (8.2)
Nitrate - 1.50 ppm (1.0)
Phosphate - 0.04 ppm (0.03)
Alkalinity - 7.4 dkh (8.5)
Calcium - 415 ppm (430)
Magnesium - 1240 ppm (1300)

Relevant livestock... (65 gallons display + sump)
6" crocea, 4" derasa and a 2" maxima clam
8" birdsnest colony
10 square inches of plating montipora
an abundance of LPS

The problem... I test my parameters every weekend after i perform a water change and last weekend I recorded the largest drop in alkalinity since I've had this tank (10 months). My alkalinity went from 8.4 dkh to 7.6 where historically my values are solid if I'm not intentionally messing with them. To correct the difference, I raised my daily dosing of reef fusion (pre-mixed two part) from 7ml a day to 8ml a day. Typically I only adjust an additional ml every few months to compensate for ongoing coral growth. This weekend I test again, and my alkalinity values are continuing to fall to 7.3 dkh.

The question... I'd like to interpret this sudden demand increase as a result of booming coral growth but I am slightly concerned that something else more detrimental may be the cause. Is it reasonable to expect to see such drops in alkalinity? I have decided to start testing every three days and I also adjusted my dose from 8 ml to 9ml in hope that my alkalinity will begin to rise. Lastly, what dkh would I start to see rapid tissue loss or in other words, the "danger zone" to avoid?

Any thoughts, advice or experience would be highly appreciated and please feel free to ask for any other details. As always, thanks for reading!

[intarsiabox]

If you are getting lots of coralline algae in your tank, it's a big alk user

[newbie2]

The drop doesn't seem all that bad if it's really only 0.3 in a week. One thing to not is that it says you are testing after a water change. It's always good to test before and after to ensure you don't get a low Alk batch of salt. Do you test the Alk of the salt after mixing prior to the water change? The Monti caps really suck up the chems once they start accelerating their growth as well

[dino]

You have 3 clams? Those will use a lot of alk and calcium.i normally test the tank and knew salt prior to water change

[IronChefItaly]

intarsiabox... bit, but its been there for a while

newbie2... 0.3dkh decrease after I had already increased the daily dose by ~14% in the week prior following the 0.8dkh decrease.

dino... true, but I would expect their calcium and alkalinity demand to be more consistent. As for my salt, I use H2Ocean and I always toss it around between buckets to ensure I've mixed whatever settlement may have happened during shipping. My mixed saltwater consistently tests around 10 dkh. Interesting points though, might be worthwhile to run a batch of tests before my waterchange, a few hours after, then the next day.

Another thought, I use 500ml dosing containers so I run nearly 3 months before having to top them off again. At the moment they're quite low so maybe the alkalinity mix separated out in the container or lost some potency?

Otherwise I'm trying to think of some change in my tank that could account for the sudden draw.

[adam84]

How many times per day is your alk dosing? (One time at 8ml per day or 2 times at 4 ml per day) also are you testing it around the same time every day?

[whatcaneyedo]

The tank is not even one year old and you've stocked it with many coral and inverts that will progressively utilize more calcium carbonate as they grow. I'd say that this increase is absolutely normal. When my former 120gal display was full of large colonies it would drop over 1 DKH per day if the calcium reactor was not running. Soon you may want to graduate to an automated DIY 2 part dosing system or calcium reactor yourself. Buying premixed additives and constantly measuring them out sounds expensive and tedious.