Alkalinity dosing and water changes on nano

[WildReefGuy]

So I have a 20 gal nano I do a water change once a week using reef crystals. I’ve noticed whenever I do my water change my calcium goes up due to the fresh salt which then I’m assuming lowers my Alk every time. I checked and my Alk was 6.8 and calcium was 480. Should I just dose Alk right after my water changes from now on and monitor?

 

[Gtinnel]

I’m not sure why you would expect your alkalinity to drop with a water change, but in short you should test it and dose alkalinity to keep your level where you want it.

 

[WildReefGuy]

I’m not sure why you would expect your alkalinity to drop with a water change, but in short you should test it and dose alkalinity to keep your level where you want it.

Because everytime I do a water change it increases the calcium to 490 or 500 ppm and I’ve heard that the more calcium you have will decrease alkalinity and when your alkalinity is high it’s likely your calcium is low. Having my calcium at a consistent range of 500 because of my water changes I assume is lowering my alkalinity

 

[MrGisonni]

Check you magnesium also. Ask @RandyHolmesFarley....he is the man when it comes to water chemistry

 

[WildReefGuy]

Check you magnesium also. Ask @RandyHolmesFarley....he is the man when it comes to water chemistry

Last week my mag was 1250

 

[MrGisonni]

All You Need to Know About: Magnesium - ATI North America

Magnesium is the silent partner of calcium and alkalinity. It plays one of the most crucial roles in a reef tank, so maintenance is essential!

www.atinorthamerica.com

1250 is probably on the low side of where most people keep their reefs. This might be leading to your instability.

 

[WildReefGuy]

All You Need to Know About: Magnesium - ATI North America

Magnesium is the silent partner of calcium and alkalinity. It plays one of the most crucial roles in a reef tank, so maintenance is essential!

www.atinorthamerica.com

1250 is probably on the low side of where most people keep their reefs. This might be leading to your instability.

Just tested its at 1330

 

[MrGisonni]

Just tested its at 1330

That's solid.

 

[MrGisonni]

Post your question in the reef chemistry forum Randy will explain

 

[Gtinnel]

Because everytime I do a water change it increases the calcium to 490 or 500 ppm and I’ve heard that the more calcium you have will decrease alkalinity and when your alkalinity is high it’s likely your calcium is low. Having my calcium at a consistent range of 500 because of my water changes I assume is lowering my alkalinity

I may be wrong but I don’t believe there is an inverse relationship between calcium and alkalinity.
Most commonly in an aquarium as one of them is dropping the other will drop as well because they’re both being consumed for stony corals to grow their skeleton. If you are doing a water change with water that has higher calcium and alkalinity levels than your tank I would expect to see both values increase. That is not saying that they will both increase to the level you want, but if your new water is adding calcium to the tank that doesn’t cause it to lower alkalinity.

 

[Randy Holmes-Farley Verified Community Expert]

I may be wrong but I don’t believe there is an inverse relationship between calcium and alkalinity.
Most commonly in an aquarium as one of them is dropping the other will drop as well because they’re both being consumed for stony corals to grow their skeleton. If you are doing a water change with water that has higher calcium and alkalinity levels than your tank I would expect to see both values increase. That is not saying that they will both increase to the level you want, but if your new water is adding calcium to the tank that doesn’t cause it to lower alkalinity.

That's correct.

The premise is an issue here.

If calcium is really dropping between water changes (you do not say how much; it may just be test error), then alkalinity MUST also be dropping. ALL mechanisms for declining calcium will drop alkalinity. Assuming the drops are not from salinity changes, then alk will typically drop by about 2.8 dKH for each 18-20 ppm calcium drop.

Consequently, the water change will be boosting alkalinity to help offset demand in the tank, not causing a drop by adding calcium.