Low Alkalinity, High Calcium but corals are still healthy!

OcellarisClown

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So I left home for two weeks and had my parents help with watching the parameters of the tank. I have a Red Sea Reefer Deluxe XXL that’s a mixed reef with large LPS colonies and tons of high-end acro mini colonies.

I immediately tested my parameters the moment I came home and I found my levels at:
Calcium-505ppm (Hanna) 510ppm (Salifert)
Alkalinity-4dkh (Hanna) 4.5dkh (Salifert)
Magnesium-1350 (Salifert)
pH-8.2
Nitrate-5ppm
Phosphate-0.02
Salinity:1.026
I understand the dynamics between calcium, magnesium, and alkalinity, but I’ve always been told to never go below 6dkh for alkalinity or ill start seeing RTN or stressed-related symptoms. So when I saw that my alk measurements were at 4-4.5 I thought my test results were inaccurate since my corals had full polyp-extension and had no signs of stress. I’m planning to gradually bringing the alkalinity back to 8-9dkh but I wanted to ask why my corals didn’t RTN under such low alk levels and how can I find out the consumption rate of calcium/alkalinity when my levels are always high but I’m still seeing growth?

My weekly water changes have kept the parameters stable and high (calcium and alkalinity are always high) but I’ve seen tanks where calcium and alkalinity are dosed daily with two-part or with Kalkwasser and consumed at such a fast rate. What am I doing wrong and why aren’t my calcium/alk levels dropping like everyone else’s tank?

Thank you so much! :)
 

P-Dub

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RTN is bacterial-based. Stressed corals will be susceptible to bacterial infections. Perhaps it occurred at such a slow rate as not to stress your corals too much. Nevertheless, I would repeat the test and confirm your initial results and up your Alk slowly to within NSW parameters and breath a sigh of relief.
 
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Spare time

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I wonder if things haven't been terrible because you are lacking nitrate and phosphate (aka you lack a decent amount of everything major needed to grow but calcium).

Then again I'd just imagine things would die rather than not grow since you need nitrogen and phosphorus in general
 
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OcellarisClown

OcellarisClown

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I wonder if things haven't been terrible because you are lacking nitrate and phosphate (aka you lack a decent amount of everything major needed to grow but calcium).

Then again I'd just imagine things would die rather than not grow since you need nitrogen and phosphorus in general
Yeah I’m trying to figure out what my nutrient level should be at (nitrates/phosphates) to keep the SPS that like clean water and LPS that like dirtier water. I tried the ULNS so that’s why my nutrient export is large with low nitrates/phosphates.
I know some reefers with mixed reefs that keep their nitrates between 10-20 so should I aim for that level?
 
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OcellarisClown

OcellarisClown

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RTN is bacterial-based. Stressed corals will be susceptible to bacterial infections. Perhaps it occurred at such a slow rate as not to stress your corals too much. Nevertheless, I would repeat the test and confirm your initial results and up your Alk slowly to within NSW parameters and breath a sigh of relief.
I’ll definitely do that! If the alkalinity levels dropped so much, was it due to the rising acidity of the water or due to the corals forming calcium carbonate?
Once alkalinity gets back to 8-9dkh I’m assuming both calcium and alk will go down due to coral growth?
 
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Randy Holmes-Farley

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I’ll definitely do that! If the alkalinity levels dropped so much, was it due to the rising acidity of the water or due to the corals forming calcium carbonate?
Once alkalinity gets back to 8-9dkh I’m assuming both calcium and alk will go down due to coral growth?

What do you mean by rising acidity?

Alk drops either by incorporation into CaCO3, or rising nitrate.
 
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OcellarisClown

OcellarisClown

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What do you mean by rising acidity?

Alk drops either by incorporation into CaCO3, or rising nitrate.
I thought once bi-carbonate/carbonic acid was formed, it wouldn’t be bio-available /absorbed by corals for skeletal growth?

I guess my real question is if my alkalinity dropped, according to my test results, does that mean it was attributed to skeletal growth or something else?

Do the alk test kits measure pure carbonate (where no H+ Ions are bound) or both including bi-carbonate (where H+ ions are bound)?
 
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Randy Holmes-Farley

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I thought once bi-carbonate/carbonic acid was formed, it wouldn’t be bio-available /absorbed by corals for skeletal growth?

I guess my real question is if my alkalinity dropped, according to my test results, does that mean it was attributed to skeletal growth or something else?

Do the alk test kits measure pure carbonate (where no H+ Ions are bound) or both including bi-carbonate (where H+ ions are bound)?

At any given alkalinity and pH, there is a exact equilibrium ratio of carbonic acid, bicarbonate, and carbonate. They interconvert extremely rapidly.

Alk drops, as I said, can be due to consumption by corals to deposit calcium carbonate, abiotic precipitation of calcium carbonate, or the production and rising of nitrate.

Alk tests measure bicarbonate, carbonate (it actually counts double), and some other things (e.g., borate).
 
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