By Bob Goemans
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Bob Goemans corresponds with John Kelly (Scotland)

John Kelly (Scotland) writes...

Dear Bob,

I want to thank you for the very quick reply regarding my problem with low pH in my 110 liter reef tank. To refresh your memory, my permutations are; live rock system, aragonite sand, skimmer, 4 power heads, 2 percula clowns, many soft/hard corals and 4 T5 lights, with the pH 7.8 - 7.9, alkalinity 13 dKH, ammonia 0, nitrite 0, nitrate 20/40 ppm, and phosphate at 0.03 ppm. And my problem was that every time I buffered with a pH powder my alkalinity went sky-high.

Based on the information originally sent, you suggested using bicarbonate of sodium/baking soda and asked for more information. Which I did use for a short time without any success, maybe I did not give it enough time (2 weeks). I therefore went back to pH buffering powder and it went up to 8.0 and raised my alkalinity. However now it is down to 7.7 - 7.8 and I fear my water has so many chemicals in it I will never get it up to 8.2 - 8.3. I have done RO water changes with quality salts, Kent Marine, ranging from 10% - 50% changes every 7- 10 days without any positive result in increasing pH.

As for my calcium level, its also down to 340 ppm, and rather than use liquid calcium like I have, I'm now dosing with Kalkwasser per manufacturers instructions thinking I could resolve both the calcium and pH problem. In upping my calcium to 400 ppm I did hope that my pH would simultaneously go up however, this is not holding true.

I was going to go back to baking soda until I tried a sample of my tank water in a 1 liter container with 1/2 teaspoon of soda and left it for 24 hours. I could not believe the result; it dropped to 7.1. Which leaves me wondering if my tank is so much full of everything but the right thing! Does this information give you any further help with my dilemma? My fear is that if I stop buffering my pH will drop even further and I will loose my corals. If there is any way you can help me with my problem it would be very much appreciated.

Thanks from sunny Scotland,

John Kelly

Bob replies...

Hi John,

And from sunny Arizona, thanks for the feedback.

Wow, wish I had all this info the first time. There's a story I tell in one of my booklets, which probably fits your situation to a "Tee." It goes like this:

"Let's use a fairly new system as an example where Kalkwasser and a buffer is being used. Alkalinity is 3.0 meq/l, slightly above the Natural Seawater (NSW) level of 2.1 - 2.5 meq/l. pH is about 8.3 and calcium is about 450 ppm. Even coralline algae are growing extremely well. At this time Kalkwasser and buffer additives are infrequently used.

In such cases a false sense of security overwhelms many reef keepers. Why make water changes if everything seems okay think some. Waste money on salt mixes when everything is so good - not me reply others! Besides, some aquarists hear that water changes aren't needed. When asked to test magnesium some reply - test what? Never heard of it! Isn't testing pH and calcium in reef aquariums sufficient they reply. Then there are those who say - hey, since everything is looking great its time for more pretty fishes.

There are now some unforeseen potholes lurking in the aquarium husbandry path. And they are quite easy to fall into unless the aquarist understands the carbonate buffering system (alkalinity). Increasing bio-load and reduced attention to certain water parameters is now setting the stage for a decline in water quality. To complicate the situation the reef keeper is reading or hearing recommendations to exceed NSW calcium and pH levels.

A few weeks later what had appeared as very good water parameters with little use of Kalkwasser and buffers now has reduced parameters. Even though they now are about what they are in the wild, they are below what they were a few weeks ago. Must be time for more additives. Right? Wrong! Kalkwasser is added to increase the calcium level back to 450 ppm and increase pH to 8.4. What's wrong with that some ask? Another good question! As noted above, to negatively impact the carbonate system simply raise pH above its NSW level of 8.2. In doing so aragonite/calcite forms as a precipitant, "reducing" available buffers in the system. When this occurs, crystals are forming somewhere in the aquarium. In a couple of days alkalinity appears to be low and it must be time for the buffer. Right? Wrong!

Buffer is added and it raises alkalinity to a higher level. However, in a couple of days pH has fallen to 8.1 and calcium is only 370 ppm. Must be time for more Kalkwasser. Right? Wrong!

There is also a concurrent possibility that coralline growth, which uses huge amounts of magnesium, is decreasing its NSW content. With less magnesium in solution, Kalkwasser increased pH now precipitates calcite and co-precipitates magnesium, further reducing an already dwindling supply of magnesium and carbonates. More crystals are forming somewhere in the aquarium. However, additional Kalkwasser has now raised calcium level to 425 ppm and pH to 8.4. Everything is again looking good. Right? Wrong! In a day or two alkalinity appears to be low and therefore the system must need some more buffer. Right? Wrong!

Bear in mind the addition of "improperly" dosed Kalkwasser masks the systems true pH for a balance between carbonate and pH equilibrium. The more one additive is added, the more it negatively affects the other additive if not dosed correctly! As more and more of these additives are used, more and more precipitates occur, clogging powerheads and turning sandbeds into concrete. Certainly not the fault of the powerheads or the sandbed!

Unless Kalkwasser is dosed correctly, achieving a reasonable calcium level is difficult. Actually, Kalkwasser contains a very small amount of calcium. In fact, at saturation it contains about 160,000 ppm less calcium than does a solution of saturated calcium chloride. Therefore much more Kalkwasser is needed to raise the calcium level and in doing so, pH can be elevated far above NSW level. Unfortunately increased pH can cause the precipitation of the very elements needed to maintain the carbonate system.

Hopefully no one perceives what is said here about Kalkwasser as being negative. It's just that it is mostly misunderstood and/or incorrectly used. If used correctly it is an excellent way to maintain alkalinity.

Testing pH, calcium, and magnesium are precursors to testing alkalinity. They go hand-in-hand like bread-and-butter so to speak. To maintain the recommended alkalinity levels first test magnesium and calcium. Keep them at NSW levels. If you do you'll find that pH will, most of the time, naturally stay at NSW levels, i.e., 8.1 - 8.2."

I would be interested in knowing the brand skimmer you have? If it's poor quality, it could be the systems oxygen content, which has a lot to do with pH, may be quite low. That's why your separate sample looked so low a day later, the dissolved O2 dissipated. Samples of water to be tested for pH need to be tested quite quickly if an accurate reading is to be attained.

Knowing what you have told me so far, I have the following recommendations. First, I'd be darn sure my pH test kit is accurate. In fact, I'd want to check pH with at least two or three different brand test kits. If it's still low, the next step involves the following: Your shimmer "MUST" be very effective, creating lots of tiny bubbles and should be operated on 24/7 basis. A real good skimmer will help raise pH simply because it oxygenates the water, which is one of its most important traits besides removing unwanted pollutes. I would also recommend using a calcium reactor containing a quality brand media (I generally recommend ARM or the Knop brand). Using old coral skeleton material or crushed coral/cheap media is a mistake. Once the skimmer and calcium reactor are properly operating, there should not be any further need for separate additives.

I would also consider purchasing an ozone generator, and Red Sea makes a nice one, even though a little expensive. Look for the one that reads the existing ORP and where you can set the unit to turn on/off as needed. Initially, shoot for a 350 REDOX. Overall water quality should improve and with the help of the skimmer and calcium reactor, pH and important items such as calcium and alkalinity should stabilize and be within correct ranges - calcium 380 - 430 ppm, and alkalinity at about 3.5 mg/l. Keep in mind you only need an 8.0 - 8.2 pH range to have a successful system. Another thing to check is your magnesium level. If there is a large swing between low and high level pH readings, chances are system alkalinity/magnesium level is low. Without sufficient buffers in the system to dampen the swing caused by increases or decreases to carbon dioxide levels between day and night, pH can experience a wide daily range. May not be the problem in your case, but I would still check it and remember, the magnesium level must relate to salinity.

Hope this helps, and keep me posted.




pH; Baking Soda

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