Help - dosed the wrong thing!!

Not sure if this was the start of my problems or not but I recently picked up a used Pinpoint pH meter and started using it a few days ago. The seller said the probe was only 3 months old so I thought it would be good for at least another 8-9months. I calibrated it using Coralife 2 part solution and everything seemed fine but I did notice I had a hard time keeping the reading constant in the 7.0 solution and it seemed to creep up .01 increments every 30 seconds or so. I didn't think too much about it at the time. After testing I put the probe in my tank and the initial reading was around 8.5. Hmmm, I thought it was high because I had been testing out at 8.3 using test strips. Before going further, here were my parameters prior to using the pH monitor;

14g nano
Ca - 350
Mg - 1110
DKh - 11
NO3 - 10ppm
NH4 - 0
Po4 - 1.0
2 – baby percula’s

My tank has been set-up for 6 weeks. I posted on here at the end of last week about my concern of my DKh being a little high but several people said it was okay and, after doing much more reading about it, I now agree.

So, back the pH. About two hours after the initial reading of 8.5 I came back into the room and noticed it had increased to 8.7. I didn't understand why the increase because I hadn't done anything. A couple hours later and it was up to 8.8?? So, in my incorrect, infinite wisdom I mixed a small batch of RO and baking soda and slowly added it to the sump area. Why did I add baking soda you're asking? I was confused - plain and simple. I'm just getting back into the hobby after several years absence and I had it backwards. I forgot that sodium bicarbonate raises pH - not lowers it . The odd thing is though the pH actually dropped to 8.4 after the dosing? Now here is where the real problem lies. When I dosed that first batch (yes, I did it a second time as well) I had my eye on the pH monitor observing the changes to make sure it was going the right way - which it was. Several hours later the monitor showed the pH had crept back up to the 8.6-8.7 range. Building on my experience earlier in the day I dosed another batch and, for the second time, the monitor showed the level had dropped back to 8.4. By last night it had again crept back up to 8.6 but before doing anything I did a full run if tests to see where the levels were. I did this also because I was getting ready to start dosing BRS's two part solution to get the Ca and Mg levels up. Needless to say the DKh reading was off the chart. Using a Salifert kit I couldn't get the color to change using 1 ml of the final regent. I believe the chart stops at 15. What do I do at this point to get the pH and DKh to come back down?

Knowing that increasing my Ca and Mg levels will help establish equilibrium with DKh I proceeded to dose the max recommended Ca and Mg supplements last night (50ppm and 100ppm respectively) to at least get those levels on the way up and hopefully start bringing the DKh back down. I dosed the Ca first and noticed very little movement of pH but when I added the Mg it dropped from 8.63 to 8.55. Should I just continue to add the max recommended dosages of Ca and Mg each day until I get those levels to target and see what effect it will have on further lowering pH and DKh or should I be more panicked and proactive and look for a more immediate solution? Also, after reading this novel does anything lead you to believe the pH probe may need replacing and isn’t working properly? Any thoughts, comments suggestions are fully welcomed.

 

I would do water changes with a quality salt mix using RO water as it is only 14g. I would say just do a couple of big water changes to sort it out; but your fish would not enjoy that. I recommend you do small water changes 10-20% each day until your parameters are in check.

I would recalibrate your pH probe in new buffer solutions, swirl in solution and let it settle then calibrate if you can. I haven't used that exact pH meter before but have used many others in the past and they usually let you calibrate them. If it doesn't then you'll just have to subtract or add to account for the error (also known as offsetting).
If in doubt compare your value against a liquid test kit, sometimes the liquid tests are easier to use than a digital for a marine tank where the pH doesn't really alter that much. When you do all other basic parameters Ca, mg, dKH you will be able to see if there is a problem or not.

Plus your pH will flutuate during the day depending on live stock, feeding times, algae photosynthesis and initial oxygenation from your protein skimmer.

 

I will try 10% water changes daily for the next couple of days to see if that helps. Thanks for that tiip.

Someone else had also suggested doising a small of a vinergar to bring the pH down so I tried that. I slowy dripped a tablesppon into the tank last night and the pH mmediately dropped from 8.75 down to 8.3. Very drastic! I wouldn't think one tbsp. would create that much of a swing? Shorly after doisng I turned the lights off for the night. When I checked the pH meter this morning it was back up to 8.55. What could be causing the level to go back up during a period of complete darkness? I don't run a protien skimmer either (no room in the 14g Biocube). Is it possible I have a bad probe? I'm tempted to buy a test kit to confirm or dispell my current reading but if I'm going to spend $20 on a quality kit I might as well just spend the extra $20 or so and get a new probe.

 

Ok... pH is directly related to dissolved CO2 in your water. At night there is no light for photosynthetic organisms to go throught photosynthesis. Your co2 increases so does your pH. Additionally your air chemistry in the room has a lot to do with this. Try openin a window near the tank and watch as ur pH goes down with the diffusion of fresh O2 into the water.

 

Take 5 min to read and understand this and it will help out a ton!
(I'm posting from iPhone so I cant do a hyperlink. U have to copy and paste)
Low pH: Causes and Cures by Randy Holmes-Farley - Reefkeeping.com

 

I would want to have it double checked just for my own peace of mind. Do you have an LFS that could test for you to confirm your results? Any local reef clubs?

 

I have one of those red pen probes for pH. You say after hours the pH rises. Are you leaving the monitor in the water for hours or testing every few hours?

I do notice mine will creep up if I leave it in the water... I ignore this. When I first put it in the water, it jumps around and levels out <- that's the number I use. After that, it will very slowly creep up and I ignore that.

EDIT: it's also my second probe. my first one, after about 8 months started jumping around erratically - regardless of water situation. I replaced it.

 

I thought Co2 decreases pH -not increase pH. Is that incorrect?

 

Good idea. There are a couple LFS near me but should they test with something more accurate than than test strips?

 

Definitely