Need help understanding low kh

Rmckoy · May 4, 2020

After testing and confirming tests results 3x
Using a new Salifert kit

Kh 6.7dkh
Cal 455
Mag 1390

Using API
Ph 7.8
Nitrate between 15-20

Besides about 20 sps frags ,
A few med size monti caps , and a pavona
I can’t really see what could be using up the alk

I use salinity salt mixed to 1.026 with Hannah salinity checker

Uncle99 · May 4, 2020

You don’t state the consumption level.
Assuming your salinity is stable.
Slowly bring Alk back to 8-8.5 dkh.
Then test each day afterwards at the same time to see what the consumption rate is.
Now you know what you have to add back.
A consumption of .5 dkh is about 9-10 ppm, not much.
SPS frags and monti surely eats up the Alk

X-37B · May 4, 2020

What alk level are you targeting?
Like Uncle99 said you need to test each day at the same time to determine how much your tank is using. Its the only way to know.
Then make your adds and test for a few days again. This way you will know your daily alk consumption.

Rmckoy · May 4, 2020

Uncle99 said:
You don’t state the consumption level.
Assuming your salinity is stable.
Slowly bring Alk back to 8-8.5 dkh.
Then test each day afterwards at the same time to see what the consumption rate is.
Now you know what you have to add back.
A consumption of .5 dkh is about 9-10 ppm, not much.
SPS frags and monti surely eats up the Alk

I have enough water mixed for a water change .

Roughly 23 gal of a 90 gal plus 30 gal volume .
Would this raise alk too fast ?

Rmckoy · May 5, 2020

Is kh consumer a lot faster than calcium ?
Does it take a specific amount of kh to consume so much calcium ...

This is the part I’m having a little trouble understanding .

Randy Holmes-Farley · May 5, 2020

I see no reason to be concerned, and would just add some alk or do some water changes (more expensive solution).

Rmckoy said:
Is kh consumer a lot faster than calcium ?
Does it take a specific amount of kh to consume so much calcium ...

This is the part I’m having a little trouble understanding .

Yes and no.

Corals depositing skeletons or abiotic precipitation of calcium carbonate. That uses about 2.8 dKH for each 18-20 ppm of calcium. A typical hobby kit easily detects a 2.8 dKH drop, but not so easily detects a 20 ppm calcium drop.

Rising nitrate levels also depletes alkalinity, and not calcium.

Rmckoy · May 5, 2020

Randy Holmes-Farley said:
I see no reason to be concerned, and would just add some alk or do some water changes (more expensive solution).

Yes and no.

Corals depositing skeletons or abiotic precipitation of calcium carbonate. That uses about 2.8 dKH for each 18-20 ppm of calcium. A typical hobby kit easily detects a 2.8 dKH drop, but not so easily detects a 20 ppm calcium drop.

Rising nitrate levels also depletes alkalinity, and not calcium.

Does the rising nitrate that depletes alkalinity also apply if macro or green hair algae is growing in a sump ?

Testing nitrates they are between 15-20 I’m also increased dosing nopox to 5ml per day

Back to my question months ago ...

Nopox or any carbon dosing effects alkalinity ?

Randy Holmes-Farley · May 5, 2020

Rmckoy said:
Does the rising nitrate that depletes alkalinity also apply if macro or green hair algae is growing in a sump ?

No, the nitrate concentration must be rising. if nitrate is steady between water changes, at any level, there is no ongoing depletion of alkalinity. A 50 ppm rise in nitrate depletes about 2.3 dKH of alkalinity.

Rmckoy said:
Testing nitrates they are between 15-20 I’m also increased dosing nopox to 5ml per day

Back to my question months ago ...

Nopox or any carbon dosing effects alkalinity ?

No, carbon dosing has no impact on alkalinity, unless nitrate is actively falling, in which case it adds alkalinity (the exact amount that was depleted when the nitrate rose initially). If nitrate is steady between water changes, at any level, with or without carbon dosing, with or without algae growth, there is no ongoing depletion or addition of alkalinity (unless the organic you are dosing is an alkalinity containing organic such as sodium acetate or calcium formate). Nopox does not contain those.