Inconsistent dKH

[AndrewRyan]

I have been using Fritz RPM salt mix recently and testing my alkalinity today I got 6.6 (3 times) with the Hanna checker.  I tested my saltwater in storage and it came up as 7.7, which is closer to the 8-9 dKH that Fritz touts as the range for 35ppt, but it is still below.  Is there something I am missing here? I don’t have any corals yet and likely won’t for some time, but I can imagine it’s not good to have low and, even worse, inconsistent dKH when I do have livestock in the system.

 

Maybe this batch is mixing up at 7.7 or so (which isn’t terrible), if that’s the case is it normal to have a 1dKH drop over two weeks with two ~10% water changes during that time?

Edited February 10, 2023 by AndrewRyan

[howaboutme]

The cycling process lowers alk so as the tank matures that effect will be minimized and you'll go to monitoring alk as a result of coral consumption, etc....

 

I'd leave it alone. Start monitoring it when you have corals. Then decide what to do. 

[AndrewRyan]

The cycling process lowers alk so as the tank matures that effect will be minimized and you'll go to monitoring alk as a result of coral consumption, etc....
 
I'd leave it alone. Start monitoring it when you have corals. Then decide what to do. 

I did not know the cycling process lowers alkalinity, but that explanation makes sense with what I’m experiencing. I am through the cycling process at this point, so I’ll do a 50% WC this weekend I suppose and see what dKH looks like a week down the road from then. Thanks.


Sent from my iPhone using Tapatalk

[AndrewRyan]

Or just wait until I have corals down the road… as you have suggested.


Sent from my iPhone using Tapatalk

[ReefdUp]

What are your Ca and Mg during the fluctuations? They're interrelated.

[Origami]

1 hour ago, AndrewRyan said:

I did not know the cycling process lowers alkalinity, but that explanation makes sense with what I’m experiencing. I am through the cycling process at this point, so I’ll do a 50% WC this weekend I suppose and see what dKH looks like a week down the road from then. Thanks.
 

Yep. An incomplete nitrogen cycle can deplete alkalinity. There's a unit of alkalinity consumed in the process of converting ammonia to nitrate (by aerobic bacteria). That unit is replaced in the process of converting the nitrate to nitrogen gas (by anaerobic bacteria). Anaerobic bacteria populations grow more slowly than aerobic bacteria, so during cycling, we often see a build up of nitrate. If we perform a water change at this stage (to reduce the nitrate), the alkalinity that was lost will never be replaced.

 

How are you testing salinity? Is your meter calibrated and, if so, with what? Finally, as Nikki noted in the post above, both calcium and magnesium is relevant here. But since this is relatively new saltwater, there *should* be sufficient magnesium in the mix to prevent abiotic precipitation; unless, of course, there was a quality control failure at Fritz - which isn't beyond the impossible. (Every once in a while you hear about a bad batch of salt coming from various manufacturers.) This, though, is pretty uncommon.

[AndrewRyan]

On 2/10/2023 at 9:37 PM, Origami said:

On 2/10/2023 at 8:10 PM, AndrewRyan said:

Yep. An incomplete nitrogen cycle can deplete alkalinity. There's a unit of alkalinity consumed in the process of converting ammonia to nitrate (by aerobic bacteria). That unit is replaced in the process of converting the nitrate to nitrogen gas (by anaerobic bacteria). Anaerobic bacteria populations grow more slowly than aerobic bacteria, so during cycling, we often see a build up of nitrate. If we perform a water change at this stage (to reduce the nitrate), the alkalinity that was lost will never be replaced.

This is fascinating and something new to me. I think I have heard elsewhere that once ammonia and nitrite levels bottom out and you detect nitrate levels in the system you should perform a large water change and then begin your regular interval water changes. I currently have undetectable ammonia and nitrite (Salifert) and 20 ppm nitrate (Hanna). But if I’m reading correctly, you are saying that I should hold off while the anaerobic bacteria begin the process of turning nitrate into nitrogen gas? If I do a large water change now I would be hindering that process? And if I allow that process to occur alkalinity will naturally be restored in the system? This is very cool stuff, please let me know if I have captured your input correctly.

 

I measured calcium and magnesium in the tank with Hanna kits.  Calcium comes in at 430 ppm and magnesium at 1485.

[Origami]

Calcium and magnesium are fine. There's no need to avoid water changes in nitrate levels become too high and you have higher life forms in the tank. Anaerobic bacteria populations develop more slowly, in part, because of nutrient limits set by diffusion. If you have no higher orders of life in the tank that could be adversely affected by high nitrates then, sure, let it sit awhile. You might even turn the temperature up to stimulate bacterial division. Continue feeding the tank, watching ammonia, nitrite and nitrate levels and, eventually, you'll see nitrate stop accumulating and begin decreasing. This is the classic sign if the anaerobic bacterial population catching up.

Sent from my Note 10+5g using Tapatalk