Floored After Calibrating pH Probe!

[smiller]

Randy,

Although I have basically given up over the last year and a half+ on fighting a pH war, I thought I was had least fallen in the low end line of OK until I calibrated the probe of my Octopus controller today. I do this every two-three months. Before I added my refugium the pH was 7.7-8.1. After adding a reverse cycle refugium less than three months ago my pH seemed to have settled at 7.85-8.0 daily. Now it appears my true reading is 7.7-7.85. I re-calibrated a second time and checked the probes straight in the calibration fluid and the #s come up on the mark. Rats.

I have followed every pH thread I have come across for ever (it seems). I have dripped kalk, bubbled cal reactor effluent, addded a second stage to reactor, opened windows with limited to no results. I have adjusted my reactor all over the dial. Never can get the son of a gun much past 6.5. The window open thing is not a good solution in east Texas. The kalk did prop up the pH, but after a few months and seeing no difference in my corals I stopped. Even with the reactor off I only get about a one point rise. My alk is always 10-11 dKH and my calcium is around 435. Bubble rate on my reactor is 28/minute and effluent rate is 20 mL/minute. Reactor effluent today shows 6.5 pH. My tank is127 gallons with 27 gallon(actual water volumn) refugium. I have mostly SPS- almost all have good color and good growth. I am closing in on two years with my only losses being three or four corals I had no business keeping. Last one was almost a year ago. Clams and fish seem healthy. I do have a small amount (10-15%) of my rock covered with red turf algae. I stopped the growth but haven't seen the thick areas die off much. I also get some light dusting of diatoms on a regular basis. Maybe a higher pH will stop this some folks say.

While I am extremely disappointed in my findings today I am as always very happy with my apparant coral health. I have never found a thread where anyone that complained about low pH also had a problem with their animals. Maybe long term? I am about ready to put myself out of my misery and throw my pH probe into the lake. If you can figure this one out you will be the first of many that have tried.
:)


Thank,
Steve

[Randy Holmes-Farley]

Steve:

<< I have never found a thread where anyone that complained about low pH also had a problem with their animals. >>

IMO, low pH is a bigger problem if the alkalinity is not higher than NSW. The issue is that calcium carbonate (coral skeletons)becomes soluble at not far from your low pH in seawater. However, if the alkalinity (read carbonate) is higher than in seawater, then that problem is reduced. That's why, IMO, CaCO3/CO2 reactor tanks do OK even when the pH drifts low.

<< I have followed every pH thread I have come across for ever (it seems). I have dripped kalk, bubbled cal reactor effluent, addded a second stage to reactor, opened windows with limited to no results. >>

I agree, it's a difficult problem to understand. Adding limewater to any tank ought to boost the pH substantially. Do you recall how much you added and what effect you got?

Is your top off water possibly acidic?

Are you sure the calibration fluids are OK? Some change over time and exposure to air. Sure the meter works right? How about the temperature compensation of the meter? What temp are the standards at, and do you know the pH of them at that temp?

[smiller]

I don't know for a fact that the pH meter is correct. I guess I could buy a pH test kit to compare but I don't really trust them. I live out in the boonies so I do not know anyone in the area that reefs to use their equipment. How long does pH hold it's value when transporting it if I was to take it to Dallas to get it checked? Nor do I know for sure if the calibration solution is good. It is the individually packaged stuff so exposure to air would not be a problem and it was bought through a company that I think turns most of their supplies over quickly.

Before I calibrated the first time I dropped the probe into the 10 solution to check the reading. It showed 10.03. I took that to mean I would be off by .03 on my new reading. I did not take a 7 reading. My old pH showed 7.89 and the new was 7.68. Does this mean anything?

Drippin kalk (nightime only) definantly did hold the pH. I could keep it close to 7.9 at night dripping 1-1 1/2 gallons. Some days were problems because I often only get 3/4 gallon of evaporation a day. I stopped because it was a pain and I couldn't see any obvious benefit. Corals looked as good at 7.7 as 7.9.

I don't understand the question about temperature compensation and standards. Sounds like something I should know.

I meant to ask in the first post and forgot...As long as the pH doesn't dip to the point of the coral skeletons becoming soluble or the swing is not too severe does pH really mean that much in terms of a healthy reef? I remember Dr. Ron telling someone that corals will adjust to whatever the pH of the tank happens to be. People (including myself) seem to get hung up on this although ill effects are not seen.


Steve

[Randy Holmes-Farley]

Steve:

<< I remember Dr. Ron telling someone that corals will adjust to whatever the pH of the tank happens to be. >>

I disagree. My reading of the literature indicates that calcification slows down a lot as the pH drops within the range we are talking about. This sounds like undesirable stress to me. Yes, they adjust by growing more slowly and possibly expending more energy to do so. That might be good for a 40-something person in New Jersey. I'm not so sure it's good for corals.


<< How long does pH hold it's value when transporting it if I was to take it to Dallas to get it checked? >>

Hard to say, because it depends on bacteria eating the organics in the water, which will drive the pH down if the container is closed (due to CO2 building up). A few hours, especially if you keep the sample cool, is not likely a problem. I've taken samples to other locations and did not see anything dramatic.

<< My old pH showed 7.89 and the new was 7.68. Does this mean anything? >>

Not that would solve our problem, no.

<< I don't understand the question about temperature compensation and standards. Sounds like something I should know. >>

There are two issues here:

1. In standards, the pKa of the ions involved will shift with temperature (there are other effects too, but this is a big one). So a pH 7 standard at 25 deg C may be 7.1 at another temperature. Over the range that we are talking, the effects are not especially large, but the standards should be used at their intended temperature (typically 25 deg C) unless you know what pH values to use for calibration at other temperatures. FWIW, some pH standards have much bigger changes with temperature than others.

2. pH probes respond differently at different temperatures. If you calibrate at the same temperature at which you take readings, this isn't an issue. But if you read pH in water at other temperatures, you need to correct the value. Most pH meters have a knob to adjust, or a digital setting for temperature, or actually have a temperature probe to use alongside the ph probe for automatic correction.

What kind of meter are you using?

<< Drippin kalk (nightime only) definantly did hold the pH. I could keep it close to 7.9 at night dripping 1-1 1/2 gallons. >>

How much Ca(OH)2 was in that 1.5 gallons?

[smiller]

I use an Octopus controller. When I calibrate the solution is much colder than the tank water, but I place the pH probe and the temperature probe in the solution.

When I was dripping kalk I used I heaping teaspoon of kalk to approx. two and one half gallons of water. I can return to dripping again-it's not a major problem other than when I am out of town.

[Randy Holmes-Farley]

<< When I was dripping kalk I used I heaping teaspoon of kalk to approx. two and one half gallons of water. I can return to dripping again-it's not a major problem other than when I am out of town.>>

You can probably up that a bit. Measuring with spoons for a solid isn't especially accurate, but the rule of thumb is on the order of 2 teaspoons per gallon of water to saturate the limewater. There's also nothing wrong with adding too much and letting it settle to the bottm (I do when using saturated limewater).

If you try saturated limewater to replace all evaporation water, and still have low pH, something is likely amiss. Even if you do this for only a week and show that the pH comes up, you've shown that you can raise the pH, and then just need to decide if you want to keep it up, and if so, but what means.

[simonh]

I have a chronically low pH around 7.7 - 7.9 is the range most of the time. Tank is around 250 litres and has a CaCO3 reactor and also around 5 litres of limewater (saturation at 10 mS measured using my conductivity probe) dosed at night for top off using a limewater stirrer. I have just recently switched to try using my reactor only in the daytime but running more effluent/CO2 to keep the alkalinity at around 3 mEq/L this seems to have improved the pH to 7.8 - 7.9 as the range.

I wondered if it was possibly my pH montior but after borrowing two pinpoint units re-calibrating all them and my aquacomputer with fresh foil sealed dated calibration soloutions from a lab supply company they all read within 0.03 of each other! After aerating outside the pH did come back up to around 8.1x.

I don't have a sump on the tank and so lack of flow down the overflow pipes and CO2 buildup in the room is likely the biggest problem (tank does have nearly 50x turnover from the flow of the pumps intank). I guess the size of the system and density of life also impacts the night pH when the animals are respiring and this seems to be more pronouced if I feed just before or after lights out and maybe due to food producing acids? or increased animal respiration? Occasionally this seems to drop the pH to 7.6 upon which I pour in a small amount of extra limewater just to boost the pH back up to 7.8 quickly and then the limewater drip seems to take it through the rest of the night fine.

At first I used to worry as all the literature suggests higher pH = faster growth. However I have not seen any negative effects on my corals. In fact most people who see any growth sequences of corals in my tank are amazed at the speed of growth. My last few calcification calculations I did using Craig Bingman's formula's indicated a rate of around 13 to 15 kg CaCO3/m2/year.

Just planning my next tank... and decided on a RDP caulrpa bed to try stabilise the pH higher and also on having a approx 400-500 litre container of water in the garage plumbed in to give a larger water volume per animal density than the current system.

[Randy Holmes-Farley]

Simon:

It doesn't surprise me too much that reactor tanks would have chronically low pH, and even that limewater alone can't completely counter it.

It would be interesting to use your tank to compare the daily "need" for CO2 provided by the limewater (to convert the OH- into HCO3-) to the daily delivery of CO2 by the reactor. Of course, much of the CO2 goes into dissolving CaCO3, but if we knew the CO2 addition rate and some measure of the CaCO3 dissolution rate, we can see what's left over (we can use the alkalinity or calcium rise in the effluent for the latter if you don't have an average CaCO3 use rate).

This would tell you whether you should still have low pH even using the limewater. Or maybe the errors involved will be too big to tell much.....

<< pronouced if I feed just before or after lights out and maybe due to food producing acids>>

Could be the food. Especially if bacteria get it, they will quickly make CO2 out of it.


<< At first I used to worry as all the literature suggests higher pH = faster growth. >>

Obviously, many people do well with low pH tanks that have a CaCO3/CO2 reactor. Maybe the higher pH described above is primarily comparing to lower pH at the same alkalinity (which is what many ocean scientists think about/obsess on: atmospheric CO2 changes on calcification rates), but perhaps higher alkalinity is actually more important than pH.

What is your typical alkalinity?

[simonh]

Randy,

I will give figures that I as still have in my spreadsheet which I was running at about a month ago (before switching to the running the reactor for 12 hours per day trial)

Tank alkalinity: 3.0 mEq/L
Effluent alkalinity: 10.7 mEq/L
Net increase: 7.7 mEq/L
Flow rate: 30 ml/min

I calculate this to be 6.1 kg CaCO3 per year using Craig's calculations. CO2 bubble rate was 30 bubbles per min. I wanted to actually measure the ml of CO2 added and Craig suggested a good way of hooking this up by putting the pipe end from the bubble counter under an upside down test tube in a bowl of CO2 saturated water. I could then calculate 1 bubble = x ml CO. However, due to the design of my Korallin calcium reactor the bubble counter isn't detachable to try this.

On the limewater side of the equation I am adding between 4.5 - 5 litres of saturated limewater depending on the time of year. I calculate 5 litres of limewater per day to be about 3.7 kg CaCO3 per year.

[Randy Holmes-Farley]

Simon:

<< CO2 bubble rate was 30 bubbles per min. I wanted to actually measure the ml of CO2 added >>

Oh, I forgot that it might be hard to measure the CO2 itself. I don't suppose that you've used up a CO2 tank in X period of time, have you?

[simonh]

I only swapped to a bigger bottle this year when things started to take off (and the pH went down) and haven't had to refil yet so I have no idea really.

[smiller]

Randy,

I have been dripping kalk at the concentration you suggested for the last 20 hours. Even at the very slow rate I have had no trouble keeping the low range near 7.9. If I had enough evaporation I'm sure I could keep it as high as I wanted to.

But again I wonder if I am wasting my time. Like simonh my corals grow at a nice rate. A couple of my montiporas have grown 3-5 times their original size in five or six months. One small capricornis has grown by at least 10 times in the same period.

I may keep dripping for awhile to compare growth rates. If things improve then I would have absolutely no problem continuing.What period of time would you think would be a good timetable for comparision? At that point if I still see little to no difference would you feel slightly more confident to say that low pH combined with a good steady alk is as healthy for corals as a higher pH combined with a lower alk? (I hear those scientific wheels grinding.;) ) Does fast growth/good color necessarily equal healthy corals? Am I still missing the boat?


Steve

[Randy Holmes-Farley]

<< But again I wonder if I am wasting my time. Like simonh my corals grow at a nice rate. A couple of my montiporas have grown 3-5 times their original size in five or six months. One small capricornis has grown by at least 10 times in the same period. >>

I'd have to agree that if the corals are growing well, we can debate till we are blue in the face about what's best for them, but if they are good enough to be happy about, that's what really matters.

<< Does fast growth/good color necessarily equal healthy corals? Am I still missing the boat? >>

I don't think your missing anything, no. there is no ultimate judge that says what is "best" (at least not that I know personally:D ). As long as they are behaving similarly to wild corals (whatever that means) and are not so stressed that a minor tank problem causes a domino effect that kills things, I can hardly argue that yours aren't perfectly fine, or that you should make any tank changes.

[smiller]

Randy,

Thanks for all of your in-depth advice.



Steve

[bzipkin]

I have 2 comments
1) I tried what you sujest only with R.O. to wash off the probe and i also tap the
probe very gently on a piece of paper towel the remove any water.
However i get 2 different readinds , 1st is if i swirl the probe in the pouch i get a
readind of .25 above the readind were i do not swirl the probe in the pouch which is correct .
To swirl or not to swirl.can someone respond to this?

2)if you have a tub with makeup R.O. water (and use this tub for water changes) put a 20 pound bag of aragonite in the bottom of it with a power head or air stone.
Here is the interesting part.
The R.O. ph is 6.8 (told to me by spectrapure lab people) which like a reactor will melt the media and RAISE your ALK , CALCUM and your PH to about 8.5 . So the more often you replace the topoff (mine is on a auto system)and do water changes the more your PH RISES.

[Randy Holmes-Farley]

However i get 2 different readinds , 1st is if i swirl the probe in the pouch i get a readind of .25 above the readind were i do not swirl the probe in the pouch which is correct . To swirl or not to swirl.can someone respond to this?

Swirl to mix and wash the probe in the calibration fluid a bit (say 10 seconds), but if swirling causes a difference while reading (which sometimes happens), take the reading with the water still. Read it the same way when measuring tank water.

The R.O. ph is 6.8 (told to me by spectrapure lab people) which like a reactor will melt the media and RAISE your ALK , CALCUM and your PH to about 8.5 . So the more often you replace the topoff (mine is on a auto system)and do water changes the more your PH RISES.

Yes , this is how some commercial products work (though they barely work).

The pH of pure water is in the 5-8 range usually, as is yours. Further, some CaCO3 will dissolve in pure water, as yours does. You don't get much in the way of calcium or alkalinity from this when you add it to a tank (maybe 40 x lower than a similar amount of limewater, depending on how you made the solution) but if you are scrapping for every bit of Ca++ and alk, it is a useful thing to do.

[bzipkin]

I have a 50 g drum ( were the aragonite is ) that tops off with R.O.and that automatically fills a 65 g refugium when evaporation has the water go below the top off probe . So allthought i have a calcium reactor (giving me tank DKH of 11 and ph of 8.1 to a low of 7.95 and calcium with a salifer shows 530 ) the PH buffering that the 50 g drum gives, is for the PH ie...8.55 with top off and all else is a bonus.

[Randy Holmes-Farley]

I agree that is a fine use. Some people use limewater (sometimes fairly dilute) in that same situation.