I emailed you about 10 yrs ago, which was the last time I had an aquarium issue! Your response really helped, so thank you. I've now had an 8 year break from marine reef keeping. Four children later, and with them now old enough to enjoy a new tank with me, I have recently setup a new reef tank (a recent holiday and visit to the Great Barrier Reef fueled our enthusiasm).
I have had a 300 litre tank setup for 3 weeks now. At the moment it is only live rock, a thin layer of coral sand, a refugium with Ecosystem Miracle Mud, some Caulerpa macroalgae, and illuminated by a compact 40W globe, and a 14K metal halide 250W light. Water movement is excellent with a new Tunze 6010 Turbelle stream. Other than some coral on the live rock and 3 snails, there is no livestock yet, at least not until the tank settles in.
I have also recently installed a Tunze calcium reactor. I have been getting readings of 500 calcium and 120mg/ml KH, even with only 1 bubble of CO2 every four seconds and affluent rate of 1 drop every 2 seconds. Some fine-tuning is needed to get the calcium level to 450 or so.
Unfortunately I am getting constant low pH readings. I have calibrated my pH meter so it should be accurate. The pH ranges from 7.95 down to 7.8, depending on the time of day, even though the refugium is lit 24 hours a day.
Why is this reading so low, even though my alkalinity according to the new test kit, so good? Is it just because it is a new tank and the chemistry will take time to settle? The grape Caulerpa I put in the refugium is dying off a reasonable amount while it takes hold.
Do I need to do something else to raise the pH? I really would like to continue to use the calcium reactor, as much of the traces of living coral on the living rock have shown clear signs of growth.
Should I hold off on getting any livestock until I sort out this low pH issue?
Wow, 10 years ago! (I must be doing something right if hobbyists remember me from one response ten years ago!) - Thanks for your update and it looks like you're off to a good beginning, as Tunze makes excellent equipment! As for the children enjoying the aquarium, I'm sure they will, and besides, I believe this hobby is extremely educational and they will learn just how important Mother Nature is and how to nourish and care for her so the world is a better place for all of us!
As for the pH situation, notice I didn't say 'problem,' as there are several aspects to take into consideration before making any changes.
Let me first begin by saying it's far better to read dKH, than KH. Keep in mind that KH (general hardness) relates to the total amount of minerals in solution, some of which have no value. So it's wiser to measure dKH Alkalinity (carbonate hardness), which is a measurement of the more 'important' buffers such as calcium and magnesium carbonates. Once you have a test kit that reads this form of alkalinity, your goal should be, if the aquarium has quite a few stony corals, about 8 - 10 dKH.
Yes, your calcium level is somewhat high at this point in time, but once the coral animals become established I would expect that level to naturally come down, with 380 - 430 ppm my preferred goal level. And since you have a quality calcium reactor, my experience has shown that if I kept its 'effluent' reading at three times the desired aquarium alkalinity level (about 25 - 35 dKH), when using one of the better calcium reactor mediums such as CaribSea ARM or the Knop product and changing that media 'at least' once per year, my aquarium calcium and alkalinity levels remained quite stable in my preferred levels, as mentioned above. Once the reactor is initially set, which does not usually take too much tweaking with good equipment; they usually stay quite stable for about six months. Then, because the good useable portion of the media is then becoming exhausted, even though there still appears to be a lot of media left in the reactor, reactors become more time consuming to maintain the desired results. And when that happens, more CO2/drip rate is required and there may become a greater disparity between proper alkalinity and calcium levels because the worthwhile portion of that media has been used up. Therefore, I always changed out my reactor media between 10 - 12 months. Believe me, this changing of the media with a 'quality' brand as mentioned above, made major differences in my systems! And I should add, do not use old coral skeleton material/crushed coral, as there are too many impurities/unusable carbonates in such products. Again, the two brands mentioned are the only ones I'll use! Furthermore, I've always purchased twin column calcium reactors, where one column was fed the CO2 and its effluent flowed through a second column filled with media allowing its low pH to become somewhat higher before dripping back into my aquarium/sump. But I've tested many reactors that have had only one column, and with those, have taken that out coming effluent and allowed it to drip through a small chamber filled with some aragonite, which was sometimes nothing more then a large syringe with its plunger removed and a piece of window screen in its bottom area, before returning to the aquarium/sump. This really helped raise that low effluent pH. So testing the reactor effluent is a requirement in properly setting them up (CO2 bubble rate and drip rate), as is a quality media and changing it far before its 'quantity' appears to be low.
Now that I've set some goals where calcium and alkalinity are involved, lets look at pH. Since this is a vital water parameter, I dislike recommending any changes until I know the hobbyist has used more than one method to test it! I've seen far different readings in letters when I asked hobbyists to try another brand test kit and/or compare their probe reading to a test kit reading. But, for the sake of moving ahead, there are factors that influence pH, and having a reactor that's using carbon dioxide is one of them, as the effluent coming from your reactor is probably quite low, e.g., in the range of 6 - 7! This can have an impact on system pH, especially in a small system such as yours. And yes, I realize your bubble rate is quite low, but so is the volume of water in your system. Other things that would affect pH would be a closed aquarium top, which would prevent good gas exchange thereby allowing dissolved CO2 acids to diminish your buffers in solution. Having a refugium with macroalgae with poor water circulation, even when oppositely lit from the aquarium, may also somewhat impact your main aquarium pH. Especially now, since your macro won't begin to flourish until that area becomes nutrient rich!
And as to pH, it is usually in the 8.0 - 8.2 range in the reef areas where much of our prized corals come from, and possibly somewhat lower in the bays and backwaters where some soft corals generally abound. So if that's good enough for Mother Nature, than that's my goal in my aquaria.
Now that I've gone this far, I should mention that I try to stay away from recommending individual liquid or powdered buffers, as they are often misused and result in precipitating calcium, which then results in that parameter needing tweaking! So, as I have done in the past, where my pH was near similar readings, I would allow my corals to be the indicator if that parameter really needed tweaking! On some systems, especially those with a single column calcium reactor and a large calcium sucking bioload, I added a small Kalkwasser stirrer, and allowed its effluent to drip through the little device I mentioned above so I would not have to add any CO2 to its effluent to reduce its 12 pH level before entering the aquarium! This helped to raise the pH coming from the calcium reactor and at the same time somewhat lower that coming from the stirrer, which further reduced any calcium reactor tweaking!
In closing, I would first recommend testing the pH with a second method/product, then test your reactor effluent and tweak to the level mentioned. Then increase the flow in the refugium 'if' necessary. Then proceed to add some bioload and recheck the pH. If still low, with low being below 8.0 during the mid portion of the aquarium's lighted timeframe, I would consider the Kalkwasser addition.
Hope this helps and keep me posted, but not ten years from now!