Relatively elevated and swinging pH – should I be concerned?

[mac622]

I maintain Ca, mG and DKh levels at 450, 1400+ and 9 respectively by dosing BRS 2-part (daily). I drip the Ca about an hour before lights out and then the DKh about an hour or two after lights out. Mg is dosed as needed (about once, maybe twice a week) I don’t run a skimmer but I perform weekly 20-30%WC’s. My lighting cycle is 10 hours for the blue LED’s and 8hours for the white LED’s and I have chaeto in a Steve T media rack that is lighted with underwater light that goes on/off in between the blue LED cycle. Let me know if I’ve missed any important details.

 

I’ve noticed that by the end of my lighting cycle the tank is reading about 8.55 to 8.60 on the Pinpoint pH meter. By the time I start dosing the DKh about 2 hours later my pH has usually fallen to about 8.35/8.45. It then shoots up to the 8.70/8.80 range while dosing the DKh (which takes about an hour) which is understandable. In the morning and before the main tank lights come on the pH normally reads around 8.1 to 8.2. Aside from the swing caused by the DKh dosing is a daily pH swing from 8.1 to 8.6 too large and reason for concern?

 

I’ve also noticed my pH is much more stable after the weekly WC. I use D-D H2Ocean salt and notice after a WC – regardless of time of day – my pH reads 8.3 and the pH swings much less in the day or two following a WC. For example, total pH swing from morning to right before lights out for the first day or two after a WC is 8.20ish to 8.45ish. As the week progresses that range gradually increases from 8.10 to 8.60. What could be causing the pH to become more unstable between WC’s?

 

Your comments are surely appreciated!

[cptbjorn]

Sounds like you are using sodium carbonate as your alk reagent which is generally recommended if your average pH is under 8.3 because it raises pH when added, you could try using sodium bicarbonate (baking soda) for a couple weeks and see how that works, it lowers pH slightly instead. Not sure if you have read it but this website has tons of good info about two part dosing.

 

Sounds like your salt mix has some kind of buffer in it that is depleted through the week somehow, I don't have any suggestions to fix that or if it even needs to be fixed though.

[mac622]

Sounds like you are using sodium carbonate as your alk reagent which is generally recommended if your average pH is under 8.3 because it raises pH when added, you could try using sodium bicarbonate (baking soda) for a couple weeks and see how that works, it lowers pH slightly instead. Not sure if you have read it but this website has tons of good info about two part dosing.

 

Correct - I used the recipe one from BRS which raises th pH. I'll give the baking soda try or order the recipe 2 mix

 

Sounds like your salt mix has some kind of buffer in it that is depleted through the week somehow, I don't have any suggestions to fix that or if it even needs to be fixed though.

 

Would you mind re-sending this link or writing the URL? The site this link brought me to was dead.

 

Thanks

[cptbjorn]

http://reefkeeping.com/issues/2006-02/rhf/index.php

 

 

Also there is a good calculator at this site, the solutions from the article above are called "Randy's Recipe 1 and 2":

http://home.comcast.net/~jdieck1/chemcalc.html