Short answer: 10-12 dKH & pH 8.3-8.4. I want consistent pH always between 8.2-8.4 as a priority.
Looooong answer: The dKH could be anywhere from 8 up to 12, what I really want is as much consistency at 8.3-8.4 as I can get. If 9dKH gets you two days at 8.2-8.4 and you’re good dosing Alk every other day, now you’ve got your target and routine set for consistency. I have been lucky to have been able to see and care for a large number of my favorite Genus of corals over the years from QT to farming. The large majority of our tanks are under 200g and we’re dosing a two part. The Alkalinity part is almost always a specific carbonate and bicarbonate blend. Tanks with a calcium reactor are specifically different in the carbonate heavy Alk they supply at a pH of about 6.5 by using CO2 to dissolve the aragonite. That results in a different water chemistry that can give the most amazing results at a lower KH and pH.
Unless, you have a controller and dosing pump for your Alk or one part, it’s your lookout to keep it steady. Since Reef tanks use Alk more than anything, it’s in a constant state of being depleted in multiple ways. Your pH is affected in a major way by the rate of the acidification of the water, oxygenation levels and the amount of CO2 from the atmosphere and decaying organic matter. The detritus in a sand bed or hidden in rocks is all the animal waste, uneaten food and everything else acidifying your water and using up KH. Then consider the amount of alkalinity and minor elements used up while coralline algae is starting to really get going and new corals are being added. On top of this, you’re being told to “not add anything you can’t test for”, “harsh chemicals” or to make micro adjustments to nitrate and phosphate and to clear up deficiencies over weeks. Nitrate and Phosphate are very important for the symbiotic zooxanthellae in the coral to supply energy via photosynthesis. What nitrate and phosphate don’t provide is all of the other necessary nutrition a coral needs like protein and fats, and Omega 3 fatty acids, amino acids, digestible Calcium other major, minor and trace elements, also some vitamins and carbohydrates only supplied through phytoplankton. This is all happening while the slow growing anaerobic bacteria responsible for breaking down nitrate and keeping nitrate from becoming toxic nitrite again aren’t well established or being added frequently to the water. People say words like “biodiversity” and “microbiome”, but they rarely tie that to the phytoplankton and other nutritional requirements for a diverse and abundant micro fauna and growth of filter feeders like sponge and tunicates.
I don’t dispute that corals can have good growth and generally better color in a lower pH down to 7.8 and KH from 7. Even if you don’t have a calcium reactor. My first focus is on an environment that is the cleanest and healthiest for all corals and invertebrates that makes acclimation easy and accelerates healing and recovery from any damage or stress. My focus on a frag tank or farming system is different and what I want from my own reef tanks is different from the other situations as well. What’s making it difficult for so many people to successfully cycle their aquarium and reach the kind of stability and growth that they want to see is the same over and over. New tanks end up in an endless fight against Dinoflagellates and tissue necrosis because of all the BS about nitrate and phosphate levels & ratio, carbon dosing, disregarding or misunderstanding pH and KH, tank biodiversity, cycling and coral nutrition is completely wrong for new aquarists who need to learn the fundamentals and how to test for and to control the major parameters. There should be no Cyano/Dino or nuisance algae problems in a properly cycled tank and coralline algae should be consistently building up before any corals are added. If you can’t grow coralline algae, you’re probably gonna have a more difficult and expensive time growing corals and it will probably seem like you have to walk a tightrope with a blindfold on to keep things just alive.
