What's going on with my Alk?

[jgvergo]

My system is 115 gallons (total volume). It's nine months old and it has a very light coral load...about 20 small frags of mixed softies and LPS. I do a 20% weekly water change using IO Reef Crystals.

I use an Apex DOS and had been dosing 80ml/day of BRS 2 part for many months. During that time my Alk was consistently around 11.0.

About a month ago I decided to bring my Alk down to 9. I naturally wanted to do it gradually, so I lowered my dosing by 10ml per week over the last 4 weeks. However, my Alk has stayed at 11.0!

I measure with a Hanna Checker and have cross checked it with a Red Sea titration tester. I clean my equipment carefully and rinse with RO/DI water between tests. How come my Alk is staying so high? It's like my dosing has no effect.

 

[iced98lx]

What is your water change water mixing up to?

 

[Diesel]

stop dosing for a few days and test every 12 hrs to see what your consumption is.
Imo with a 20% WC weekly and only have a few frags you don’t need to dose yet.

But let’s see how much it drops first.

 

[jgvergo]

What is your water change water mixing up to?

My new water is 12.3

 

[jgvergo]

stop dosing for a few days and test every 12 hrs to see what your consumption is.
Imo with a 20% WC weekly and only have a few frags you don’t need to dose yet.

But let’s see how much it drops first.

Thanks, I'm going to do this...stay tuned

 

[iced98lx]

agree with diesel at this point with your inhabitants tank size of water changes it's unlikely that you would need to actually dose at all. Especially so considering how high the elk is in your will change water. wholeheartedly agree with the suggestion of stopping dosing completely and monitoring out the calcium over the next week. Do you have time to test alkalinity daily?

 

[iced98lx]

Sorry for the typos voice to text what is your current calcium level and your change water calcium level?

 

[Randy Holmes-Farley Verified Community Expert]

The demand for daily alk additions rises as the alk rises. At 11 dKH, you need a lot more than you need at 9 dKH just to maintain levels.

 

[jgvergo]

agree with diesel at this point with your inhabitants tank size of water changes it's unlikely that you would need to actually dose at all. Especially so considering how high the elk is in your will change water. wholeheartedly agree with the suggestion of stopping dosing completely and monitoring out the calcium over the next week. Do you have time to test alkalinity daily?

I will make the time to test daily!

 

[jgvergo]

Update: It's been a week without dosing. My alkalinity readings are in this chart:

The horizontal axis is the number of hours since I stopped dosing and the vertical axis is dKH. The line is a linear regression. Basically, the dKH dropped 0.3 per day. My total water volume is 85 gallons, including my sump, live rock, sand and equipment.

But wait...it gets more complicated! Based on some recent R2R posts, I think I'd like to target a dKH of 8.5.

My newly mixed salt water has a dKH of 12.1. After a 20% water change, the dKH of my tank rose from 8.0 to 8.7. So any time I do a water change my Alk is likely to jump 0.7 dKH!

That means that I should target an AVERAGE dKH of 8.5. Right before a water change, it should bottom out at about 8.1. After a WC, it will jump to 8.8. That means over the course of the week, I should dose enough Alk to allow it to slowly decrease from 8.8 to 8.1 with dosing.

So I believe it comes down to this:
1) Corals use 0.3 dKH/day
2) I should let the actual dKH drop 0.1 dKH/day
3) Therefore, I need to dose enough to "add" 0.2 dKH/day. This is actually enough to offset the 0.3 dKH drop to make it 0.1 dKH/day.

I used the BRS Alkalinity calculator (I selected the Liquid Soda Ash, New Pharma Pouch options because I dose liquid after mixing from the pouch) and determined that I need to dose 12.1 ml per day.

Make sense???