Understanding Test Results...

[Dom]

On 8/14, I did a round of testing and received the following results:

pH: 8.35
Nitrates: 20
Phosphates: .5
Nitrites: 0
Ammonia: 0
Salinity: 35ppt
KH: 5.6
Ca: 420

Although not too terrible, I wasn't happy with the nitrate and phosphate result. Additionally, I like my KH in the 8-12 range.

I did a 10% water change and allowed the water to circulate (12 hours) while using this calculator to determine how much baking soda to dose.

I completed the mixture (which called for 13.6 grams) and supplemented, monitoring pH to be certain not to fluctuate beyond .20.

Today, I did another round of tests:

pH: 8.53 - I attribute this increase to the baking soda. Is this conclusion correct?

Nitrates: 20 - No change. I did another 10% water change.

Phosphates: .5 - No change.

Nitrates: 0

Ammonia: 0

Salinity: 37ppt - Oops... too much salt mix.

KH: 9 - Falls within my target range.

Ca: 460 - Has this increased due to the increased salinity?

As I understand it, Alkalinity and Calcium are inversely proportional. I've increased my Alkalinity; shouldn't my calcium have gone down?

I guess what I'm asking is this:

Does the effect of salinity on calcium supersede the effect of alkalinity on calcium?

 

[CodyRVA]

following

 

[Cory]

Its probably testing error. Or your magnesium is really high preventing any precipitation, since your salimity is 37ppt, mag should be higher. Precipitation mainly occurs when too much alkalinity is added or too much high ph alkalinity supplement is added. Imo.

 

[Dom]

Its probably testing error. Or your magnesium is really high preventing any precipitation, since your salimity is 37ppt, mag should be higher. Precipitation mainly occurs when too much alkalinity is added or too much high ph alkalinity supplement is added. Imo.

Well... pH is tested by a properly calibrated meter. I test uausing an API kit which is not expired and KH using a Red Sea test kit. I don't test Mag, but probably should.

While I appreciate the response to my post, I'm not sure you've answered my question. If you have, I'm not understanding your answer.

 

[CindyKz]

Hard to say without knowing what's in your tank or what salt mix you're using, but if you use a salt mix that is high in Ca you may have raised it with the water changes.

Alk and Ca are directly, not inversely, proportional, but we use more units of alk than we do of Ca so we see changes in alk more quickly in our measurements.

To my knowledge salinity has no effect on Ca other than as I said above, different salt mixes have different levels of Ca added. Someone with more tank chemistry knowledge may need to correct me!

Hth.

 

[Michael Montgomery]

Question: How do the corals look? If you dont think something is right, Why doesnt it look right ? Describe or post a pic.

ooooooorrr are you chasing numbers?

For ME... Nitrates at 20 isnt bad....
However... Those phosphates seem WAY high..!!!

 

[Dom]

Question: How do the corals look? If you dont think something is right, Why doesnt it look right ? Describe or post a pic.

ooooooorrr are you chasing numbers?

For ME... Nitrates at 20 isnt bad....
However... Those phosphates seem WAY high..!!!

There is something I've failed to make clear:

I am perfectly happy with the numbers I'm just trying to understand the change that took place AFTER the water change.

 

[Cory]

Well... pH is tested by a properly calibrated meter. I test uausing an API kit which is not expired and KH using a Red Sea test kit. I don't test Mag, but probably should.

While I appreciate the response to my post, I'm not sure you've answered my question. If you have, I'm not understanding your answer.

Yes an increase in salinity will increase all elements. So calcium would increase for sure.

 

[Dom]

Question:
However... Those phosphates seem WAY high..!!!

Yes I am inclined to agree with you on phosphates, which is why I did the WC, but I wasn't terribly worried.

I just moved my setup to a new stand. My sump includes a refugium for nutrient export, but right now, it only has a deep sand bed. Once I put macro in it, I'm certain it will come down.

 

[chipmunkofdoom2]

As I understand it, Alkalinity and Calcium are inversely proportional. I've increased my Alkalinity; shouldn't my calcium have gone down?

If your magnesium is low, your calcium and carbonate alkalinity levels could become unstable because they are more likely to join and precipitate out of solution, lowering both calcium and alkalinity. But do not necessarily have an inverse relationship. Adding carbonate alkalinity supplements could cause calcium to go down by encouraging precipitation, but this only occurs under certain situations. This table in Randy Holmes-Farley's article on the subject is a good reference.

Does the effect of salinity on calcium supersede the effect of alkalinity on calcium?

Again, this could be technically correct, but it depends upon your exact meaning. Let's your salinity is 35ppt and your calcium is 450ppm. If you add enough freshwater to reduce your salinity to 33ppt, this is a reduction of about 6%. Because you are diluting your aquarium water by adding fresh water, the concentration of all elements will be diluted. The same amount of NaCl, Mg, Ca, CaCO3, etc still exist. They're just dissolved in more water, meaning the concentration has been reduced. The calcium, which was 450ppm @ 35ppt, would now be around 425ppm @ 33ppt salinity. Your calcium didn't necessarily drop: the amount of calcium wasn't reduced. The amount of water in which the calcium is dissolved increased, making the concentration lower. The same works in reverse. Let's say your salinity is 35ppt and you increase your salinity by allowing water to evaporate to 37ppt. That's about 6% higher than 35ppt. Your calcium, which was 450ppm, would now be 475ppm. Again, there is no more calcium. It's the exact same amount as you had before. However, there is just less water and the same amount of calcium, so the overall concentration goes up.

TL;DR: Under normal circumstances, adding carbonate alkalinity supplements won't necessarily cause precipitation of calcium, but it is possible. Raising salinity typically raises the concentration of most elements in artificial seawater simply because salt mixes have balanced levels at 35ppt salinity. If you increase the salinity, there will be more of all the elements in the salt mix, calcium included. If you dilute the saltwater below 35ppt salinity, you will see lower concentrations of all elements, including calcium.