How quickly can I lower alkalinity?

[Cunning_plan]

I am looking to lower my alkalinity from 12.2 to 8. I plan to do this using water changes of a lower alkalinity salt (8 dkh). Over what window should I do this to prevent a crash.

For context, I've only recently started regular testing of alkalinity as I had little in the tank that was taking it up and my normal water changes kept it stable at around 8.5. over Christmas I was away for 3 weeks and had my auto feeder set to a bit too heavy. This meant my nitrates were at around 60 and I had an algae outbreak. To combat this I did a whole bunch of water changes and installed a refugium at last.

Having decided to start looking at some more difficult corals I decided to understand in more detail what my alkalinity usage looked like. Upon testing I found it to suddenly have jumped to 12.2. I eventually narrowed this down to being due to a bad batch of salt - my blue bucket was mixing to 12.0 and my calcium and mag were also high.

I have verified both my salinity (Hanna electronic and red sea refractometer, both fresh calibrated) and my alkalinity (Hanna and salifert) so feel confident in my conclusion. That said if I have missed anything please do tell.

 

[DC Reefer]

Doesn't sound like you are doing Alk. What inhabitants do you have in the tank currently? If no sensitive corals you could get away with 10-15% water changes each day to bring it down to where you wanted it. As you get closer to your goal, you could do larger water changes. If not sensitive corals you could probably go faster.

I would also have my salinity tested at my LFS to get a 3rd opinion on the salinity

 

[Cunning_plan]

Doesn't sound like you are doing Alk. What inhabitants do you have in the tank currently? If no sensitive corals you could get away with 10-15% water changes each day to bring it down to where you wanted it. As you get closer to your goal, you could do larger water changes. If not sensitive corals you could probably go faster.

So it's largely soft corals, a couple of monti caps, a couple of torches and an acan.

I would also have my salinity tested at my LFS to get a 3rd opinion on the salinity

Sadly with lockdown that's not really viable for me. I bought fresh calibration solutions for both my hanna and my refractometer however so am fairly convinced.

Red Sea technically let you check the ICP test for your batch of salt. Unfortunatley my bucket doesn't actually have a batch number!

 

[Randy Holmes-Farley]

Unless nutrients are very low, the alk is not an emergency. Red Sea recommends alk levels this high for fastest coral growth.

If you want it lower, can you just let it slowly fall on its own?

 

[blasterman]

I would let it fall on it's own.

Reef Crystals has tested higher than this for me depending on batch.

However, monti caps in particular aren't thrilled about high alk swings. I would just switch to a more 'Pro' category salt which have alk values in the 8-9 range, or just use Instant Ocean.

Use up your current salt as a fractional percent of the newer salt.

 

[Cunning_plan]

Unless nutrients are very low, the alk is not an emergency. Red Sea recommends alk levels this high for fastest coral growth.

If you want it lower, can you just let it slowly fall on its own?

Nitrate and phosphate are both very low as I have had algae issues in the past. The tank doesn't use enough alk to let it fall at and sane rate - 0.025 dkh a day.

Call and mg were also above range so I'm worried what else could be wrong I'm not seeing.

 

[Randy Holmes-Farley]

Nitrate and phosphate are both very low as I have had algae issues in the past. The tank doesn't use enough alk to let it fall at and sane rate - 0.025 dkh a day.

Call and mg were also above range so I'm worried what else could be wrong I'm not seeing.

Very low means what?

If it is less than 0.02 ppm phosphate or 2 ppm nitrate, I'd feed heavily until the alk declines if you have SPS. YOU want to avoid burnt tips.