High Alkalinity or Not?

[griss]

To start with being honest, for the last year or so, I've been really lax about testing.

My system is a 92 gallon corner bow front, 6" DSB, approx. 80 lbs live rock, 55 gallon sump/fuge. For a total water volume of about 100 gallons. I have a very low bio-load.

I recently made the commitment to regularly test. So, I acquired new test kits (Salifert) for pH, Alk, Calcium and Magnesium.

On 4/24/14 I tested and these were the results.
pH 8.0
Alk 8.9 dKH
Ca 420
Mg 1170

So, pH and Ca are okay, Mg is a little low, but Alk is a bit high.

On 4/27/14 I did a 20 gallon water change. I use Coralife salt with RO/DI (all new cartridges, DI resin and RO membrane) and mix to a Specific Gravity of 1.025. At this time, I also changed out the GFO (DFS) and GAC (BRS) in my BRS reactor. When I do this, I flush the GFO and GAC with about 5 gallons of tank water as part of the water change.

Note, I recharge my GFO with Roebic Lye using 10 Tsp per liter of RO/DI water. Total volume of solution depends on how much GFO I'm regenerating. I recharge for 3 days (mixing daily), then flush with about 10 gallon of fresh RO/DI water before storing for the next use.

Tonight, I checked parameters and here's where they fell on the first test.

pH 8.0
Alk 11.5 dKH
Ca 430
Mg 1230

Wait, what? 11.5 Alk? So, I retested and got an Alkalinity of 9.3. Again, wait, something is not right here.

So, I used the test solution that comes with the Salifert kit. First test yielded a result of 8.0 when it should have been 6.7. So, I cleaned everything and retested with the test solution and go a result of 6.4.

Any suggestions on what's going on here? User error? Not cleaning the test vials/syringes good enough? Using too much lye because I misread the thread on recharging GFO? Not rinsing the regenerated lye enough?

 

[bertoni]

Hmm, I'd guess that the vial had an accumulation of calcium carbonate, maybe, or something that was adding alkalinity. The titrant is an acid, so it'll measure the calcium carbonate it dissolves as part of the total alkalinity.

The GFO might have had some lye in it. The reef chemistry calculator doesn't have a lye entry in it, but ½ tsp might have raised the dKH by 1 unit or so, I think, depending on the water volume. I'm guessing it's very roughly twice as strong as sodium carbonate.

If you want to check the GFO, rinsing with a bit of vinegar probably would help remove more lye, but I don't think it should be necessary.

 

[griss]

Thanks Jonathan

 

[bertoni]

You're welcome!

 

[tmz]

It takes a lot of rinsing to remove the lye to a point where the soapy feel is gone.

 

[Reefvet]

On 4/24/14 I tested and these were the results.
pH 8.0
Alk 8.9 dKH
Ca 420
Mg 1170

So, pH and Ca are okay, Mg is a little low, but Alk is a bit high.


pH 8.0
Alk 11.5 dKH
Ca 430
Mg 1230

It seems you've had your question answered. So I hope you don't mind my going off topic. I'm curious you why you think an alkalinity of 8.9 dKH is high ?

Yes it's a bit higher than NSW, but not significantly.

 

[Randy Holmes-Farley]

So, I used the test solution that comes with the Salifert kit. First test yielded a result of 8.0 when it should have been 6.7. So, I cleaned everything and retested with the test solution and go a result of 6.4.

Could just be poor testing skills. Maybe you need more practice. :lol:

 

[griss]

It takes a lot of rinsing to remove the lye to a point where the soapy feel is gone.

Guess I need to rinse a bit better in the future. Thanks Tom.

It seems you've had your question answered. So I hope you don't mind my going off topic. I'm curious you why you think an alkalinity of 8.9 dKH is high ?

Yes it's a bit higher than NSW, but not significantly.

I guess I was more concerned with the variance in the test results than, the result being a "bit" high compared to NSW. Poorly worded thread title on my part

Could just be poor testing skills. Maybe you need more practice. :lol:

That's very likely Randy:lol:

 

[tmz]

You are welcome George.
I don't know if you could get enough sodium chloride from the regenerated gfo to make large differnece in alk . I rinse mine five times with ro water before use. Sometimes it still has a very sight soapy feel. I only use relatively small amounts of gfo though and see no effect on alkailiny.

 

[griss]

You are welcome George.
I don't know if you could get enough sodium chloride from the regenerated gfo to make large differnece in alk . I rinse mine five times with ro water before use. Sometimes it still has a very sight soapy feel. I only use relatively small amounts of gfo though and see no effect on alkailiny.

I've been changing out my GFO every 2-3 weeks as I've been battling some hair algae. When I do, I fill an entire BRS reactor canister with GFO.

Mine does still feel soapy after rinsing. So, I think I might need to rinse a little more.

When I'm done regenerating, I rinse with about 10 gallons of fresh RO/DI. Then put in storage.

I change out the GFO and GAC as part of my water change. I remove the old, fill the BRS canisters with regenerated GFO and fresh GAC. Then, I run 5 gallons of tank water through the reactor into a 5 gallon bucket and discard the contents of the bucket.

However, like you said, there is probably isn't enough to affect alkalinity.

That said, I was more perplexed by the variance in the test results. As Randy pointed out, that was probably user error