Still confused about testing

[Blue Meg]

i only live a few blocks from my lfs and they test for free. But one day someone was talking about pH, calcium, and alkalinity.

I used to assume that pH and alkalinity were the same thing as they were often used interchangeably in chem lab in college. A solution with a pH of 12 was an alkaline solution for example. Now it seems to be calcium? And then they also did a calcium test? What gives?

 

[Bayareareefer18]

i only live a few blocks from my lfs and they test for free. But one day someone was talking about pH, calcium, and alkalinity.

I used to assume that pH and alkalinity were the same thing as they were often used interchangeably in chem lab in college. A solution with a pH of 12 was an alkaline solution for example. Now it seems to be calcium? And then they also did a calcium test? What gives?

Yes anything over a ph of 7 would be considered alkaline. Alkalinity is the measure of carbonate and bicarbonate in the water (carbonate hardness) which is your ph buffer

Do you keep corals ?

 

[Blue Meg]

Yes anything over a ph of 7 would be considered alkaline. Alkalinity is the measure of carbonate and bicarbonate in the water (carbonate hardness) which is your ph buffer

Do you keep corals ?

I do keep corals. I’m in a bit of a tank issue right now, so the guys at the fish store who service reef tanks owned by businesses are periodically coming by to give me tutorials and help me with equipment advice. It’s cheaper than killing stuff all the time and better than describing issues at the store.

I only have one sps...a monti who is happy. I have lps and zoas mostly. My goal is a happy tank with 20% sps, 40% lps, and 40% soft. I’m still bewildered at what lives and dies. I had a colony of sunny Ds that thrived and died and on another rock I have some rainbow hornets that went from four to 100 in a year.

 

[Randy Holmes-Farley]

i only live a few blocks from my lfs and they test for free. But one day someone was talking about pH, calcium, and alkalinity.

I used to assume that pH and alkalinity were the same thing as they were often used interchangeably in chem lab in college. A solution with a pH of 12 was an alkaline solution for example. Now it seems to be calcium? And then they also did a calcium test? What gives?

Alkaline (as a qualitative measure of pH) and alkalinity (a measure of bicarbonate and carbonate) are related, but not interchangeable terms.

These have more:

Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley
https://www.reef2reef.com/threads/o...-reef-aquarium-by-randy-holmes-farley.173563/

Calcium

Many corals use calcium to form their skeletons, which are composed primarily of calcium carbonate. The corals get most of the calcium for this process from the surrounding water. Consequently, calcium often becomes depleted in aquaria housing rapidly growing corals, calcareous red algae (coralline algae), Tridacnids (clams) and Halimeda (a macroalgae containing calcium carbonate). As the calcium level drops below 360 ppm, it becomes progressively more difficult for these organisms to collect enough calcium, thus stunting their growth.

Maintaining the calcium level is one of the most important aspects of coral reef aquarium husbandry. Most reef aquarists try to maintain approximately natural levels of calcium in their aquaria (~420 ppm). It does not appear that boosting the calcium concentration above natural levels enhances calcification (i.e., skeletal growth) in most corals.

For these reasons, I suggest that aquarists maintain a calcium level between about 380 and 450 ppm, although higher is generally not a problem until it gets so high that calcium carbonate precipitation becomes problematic. Aquarists with a very light demand may be able to maintain calcium with water changes, especially since some salt mixes have excessive calcium in them. But most established aquaria with growing hard corals and coralline algae will require some calcium supplementation, and in some cases, it might be needed every day.

I usually suggest using a balanced calcium and alkalinity additive system for routine maintenance. The most popular of these balanced methods include limewater (kalkwasser), calcium carbonate/carbon dioxide reactors, and the two-part or three-part additive systems for calcium and alkalinity. If calcium is depleted and needs to be raised significantly, however, such balanced methods are not a good choice since they will raise alkalinity too much. In that case, adding calcium chloride is a good method for raising calcium in a one-time correction.

Alkalinity

Like calcium, many corals also use "alkalinity" to form their skeletons, which are composed primarily of calcium carbonate. It is generally believed that corals take up bicarbonate, convert it into carbonate, and then use that carbonate to form calcium carbonate skeletons. That conversion process is shown as:

HCO3- → CO3-- + H+

Bicarbonate → Carbonate + proton (which is released from the coral)

To ensure that corals have an adequate supply of bicarbonate for calcification, aquarists could just measure bicarbonate directly. Designing a test kit for bicarbonate, however, is somewhat more complicated than for alkalinity. Consequently, the use of alkalinity as a surrogate measure for bicarbonate is deeply entrenched in the reef aquarium hobby.

So, what is alkalinity? Alkalinity in a marine aquarium is simply a measure of the amount of acid (H+) required to reduce the pH to about 4.5, where all bicarbonate is converted into carbonic acid as follows:

HCO3- + H+ → H2CO3

The amount of acid needed is equal to the amount of bicarbonate present, so when performing an alkalinity titration with a test kit, you are “counting†the number of bicarbonate ions present. It is not, however, quite that simple since some other ions also take up acid during the titration. Both borate and carbonate also contribute to the measurement of alkalinity, but the bicarbonate dominates these other ions since they are generally lower in concentration than bicarbonate. So knowing the total alkalinity is akin to, but not exactly the same as, knowing how much bicarbonate is available to corals. In any case, total alkalinity is the standard that aquarists use for this purpose.

Unlike the calcium concentration, it is widely believed that certain organisms calcify more quickly at alkalinity levels higher than those in normal seawater. This result has also been demonstrated in the scientific literature, which has shown that adding bicarbonate to seawater increases the rate of calcification in some corals. Uptake of bicarbonate can consequently become rate limiting in many corals. This may be partly due to the fact that the external bicarbonate concentration is not large to begin with (relative to, for example, the calcium concentration, which is effectively about 5 times higher).

For these reasons, alkalinity maintenance is a critical aspect of coral reef aquarium husbandry. In the absence of supplementation, alkalinity will rapidly drop as corals use up much of what is present in seawater. Water changes are not usually sufficient to maintain alkalinity unless there is very little calcification taking place. Most reef aquarists try to maintain alkalinity at levels at or slightly above those of normal seawater, although exactly what levels different aquarists target depends a bit on the goals of their aquaria.

Interestingly, because some corals may calcify faster at higher alkalinity levels, and because the abiotic (nonbiological) precipitation of calcium carbonate on heaters and pumps also rises as alkalinity rises, the demand for alkalinity (and calcium) rises as the alkalinity rises. So an aquarist generally must dose more calcium and alkalinity EVERY DAY to maintain a higher alkalinity (say, 11 dKH) than to maintain 7 dKH. It is not just a one-time boost that is needed to make up that difference. In fact, calcification gets so slow as the alkalinity drops below 6 dKH that reef aquaria rarely get much below that point, even with no dosing: natural calcification has nearly stopped at that level.

In general, I suggest that aquarists maintain alkalinity between about 7-11 dKH (2.5 and 4 meq/L; 125-200 ppm CaCO3 equivalents). Many aquarists growing SPS corals and using Ultra Low Nutrient Systems (ULNS) have found that the corals suffer from “burnt tips†if the alkalinity is too high or changes too much. It is not at all clear why this is the case, but such aquaria are better served by alkalinity in the 7-8 dKH range.
As mentioned above, alkalinity levels above those in natural seawater increase the abiotic precipitation of calcium carbonate on warm objects such as heaters and pump impellers, or sometimes even in sand beds. This precipitation not only wastes calcium and alkalinity that aquarists are carefully adding, but it also increases equipment maintenance requirements and can “damage†a sand bed, hardening it into a chunk of limestone. When elevated alkalinity is driving this precipitation, it can also depress the calcium level. An excessively high alkalinity level can therefore create undesirable consequences.

I suggest that aquarists use a balanced calcium and alkalinity additive system of some sort for routine maintenance. The most popular of these balanced methods include limewater (kalkwasser), calcium carbonate/carbon dioxide reactors, and the two-part/three part additive systems.

For rapid alkalinity corrections, aquarists can simply use baking soda (sodium bicarbonate) or washing soda (sodium carbonate; baked baking soda) to good effect. The latter raises pH as well as alkalinity while the former has a very small pH lowering effect. Mixtures can also be used, and are what many hobby chemical supply companies sell as “buffersâ€. Most often, sodium carbonate is preferred, however, since most tanks can be helped by a pH boost.

pH

pH is a measure of the concentration of protons (H+ ions) and hydroxide (OH-) ions in the water. Aquarists spend a considerable amount of time and effort worrying about, and attempting to solve, apparent problems with the pH of their aquaria. Some of this effort is justified, as true pH problems can lead to poor animal health. In many cases, however, the only problem is with the pH measurement or its interpretation. Moreover, the maintenance of appropriate alkalinity in seawater goes a long way to ensuring that the pH is acceptable, with just a couple of exceptions that will be discussed below.

Several factors make monitoring a marine aquarium's pH level useful. One is that aquatic organisms thrive only in a particular pH range, which varies from organism to organism. It is therefore difficult to justify a claim that a particular pH range is "optimal" in an aquarium housing many species. Even natural seawater's pH (8.0 to 8.3) may be suboptimal for some of its creatures, but it was recognized more than eighty years ago that pH levels different from natural seawater (down to 7.3, for example) are stressful to fish. Additional information now exists about optimal pH ranges for many organisms, but the data are inadequate to allow aquarists to optimize pH for most organisms which interest them.

Additionally, pH's effect on organisms can be direct, or indirect. The toxicity of metals such as copper and nickel to some aquarium organisms, such as mysids and amphipods, is known to vary with pH. Consequently the acceptable pH range of one aquarium may differ from another aquarium, even if they contain the same organisms, but have different concentrations of metals.

Changes in pH nevertheless do substantially impact some fundamental processes taking place in many marine organisms. One of these fundamental processes is calcification, or deposition of calcium carbonate skeletons, which is known to depend on pH, usually dropping as pH falls. At a low enough pH (somewhere below pH 7.7) coral skeletons can begin to slowly dissolve. Using this type of information, along with the integrated experience of many hobbyists, we can develop some guidelines about what is an acceptable pH range for reef aquaria, and what values push the limits.

The acceptable pH range for reef aquaria is an opinion rather than a clear fact, and will certainly vary with the opinion's provider. This range may also be quite different from the "optimal" range. Justifying what is optimal, however, is much more problematic than is justifying that which is simply acceptable, so we will focus on the latter. As a goal, I'd suggest that the pH of natural seawater, about 8.2, is appropriate, but coral reef aquaria can clearly succeed in a wider range of pH values. In my opinion, the pH range from 7.8 to 8.5 is an acceptable range for reef aquaria.

In truth, many aquarists never measure pH, and many that do so do not do anything with the results they obtain. This lack of action is usually okay, as most aquaria do not naturally fall outside of the acceptable ranges. Times when it is most important to at least check pH once in a while are:

1. When using very high pH additives, such as limewater (kalkwasser). In this case, one should ensure that the pH does not get above about 8.55. At higher values, the precipitation of calcium carbonate on pumps and such can become excessive. Every 0.3 pH unit rise in pH is equivalent to about a doubling of the calcium or alkalinity value in terms of the likelihood of precipitation of calcium carbonate (because bicarbonate turns into carbonate as the pH rises, driving precipitation). Aquaria may often get to a pH that is high enough to double the precipitation rate due to elevated pH, but one does not often see aquaria with calcium or alkalinity that is double the normal value, making high pH a big driver of precipitation.

2. When the air around the aquarium has elevated carbon dioxide levels, such as in a newer, tighter home. Low pH due to elevated carbon dioxide in the air is VERY common. While it may be useful to ensure the pH stays above 8.0, there are many fine aquaria with the bottom end of the pH range at pH 7.8. Below that value, I'd want to take more aggressive action, such as more fresh air in the home, top off with limewater (kalkwasser), a fresh air line from outside to a skimmer inlet, or a CO2 scrubber on a skimmer inlet.