White build up on my heater
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Randy Holmes-Farley
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Right, calcium carbonate:
What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com
Precipitates on Heaters and Pumps
The precipitate that forms on heaters (Figure 2) and pumps is primarily calcium carbonate. Natural seawater and reef aquarium water is often supersaturated with calcium carbonate, but the precipitation is kept at a very slow pace, primarily by magnesium ions (for reasons described later in this article). Certain factors, however, push the supersaturation even higher, and the "pressure" to precipitate becomes too high for the magnesium to prevent it. These factors include elevated calcium, alkalinity, pH, and in the case of heaters and pumps, elevated temperature. How these factors impact supersaturation is detailed later in the article, but the following section summarizes the effects.
Chief among the factors causing precipitation are alkalinity and pH. While most aquarists would be unlikely to have in their aquaria double the calcium level of natural seawater (more than 800 ppm), many folks have doubled its supersaturation level via alkalinity and pH. With all other things being similar, for example, an aquarium with a pH of 8.5 has twice the supersaturation of one with a pH of 8.2, and an aquarium with a pH of 8.2 has twice the supersaturation of one with a pH of 7.9.
Alkalinity, likewise, can be a big contributor to precipitation. Many aquarists push alkalinity to elevated levels, approaching or exceeding twice the naturally occurring levels (about 2.5 meq/L, or 7 dKH). That change can, in turn, double the supersaturation.
Elevated temperature impacts calcium carbonate precipitation in two ways: 1) by simply reducing the solubility of CaCO3 (which is more soluble at lower temperatures) and 2) by causing the formation of additional carbonate from the bicarbonate in solution. These effects are roughly similar in magnitude, and are one of the reasons that pumps and heaters can be more rapidly coated with calcium carbonate precipitate than other objects in the same aquarium.
Another possible reason that pump impellers and heaters get coated more rapidly than other surfaces is that such surfaces may be less likely to become coated with a film of bacteria that prevent calcium and carbonate from reaching the surface. Heaters may become too hot for such bacterial films to form properly, and pump impellers may have enough water motion around them to wash away bacteria as soon as they begin to attach. Exactly how large such effects are, however, is not clear to me.
Low magnesium can also contribute to precipitation because magnesium interferes with the precipitation of calcium ions. Normally, magnesium ions slip into spots where calcium would otherwise bind, altering the surface's structure so that it no longer is a good seed crystal for further calcium carbonate precipitation. Fewer magnesium ions in solution makes this process less effective.
Finally, it appears that ferric ion (Fe+++) may help initiate the precipitation of calcium carbonate. Such ions may be added directly in some products, and can be released from iron-based phosphate binders such as Rowaphos, Phosban, and Phosphate Killer.
Preventing Precipitates on Heaters and Pumps
While the calcium carbonate that precipitates onto heaters and pumps can be readily removed by soaking them in acid (undiluted vinegar or diluted muriatic acid/hydrochloric acid: 1 part acid added to 9 parts fresh water), it is often easier to prevent the buildup in the first place. The following actions can be taken if the aquarium has excessive precipitation of calcium carbonate:
Note: actions 1, 3, and 4 may also make it harder for calcifying organisms such as corals and coralline algae to calcify, so they may grow more slowly if a significant reduction is made in pH, calcium or alkalinity.
1. Reduce the overall pH. The lower the better for this purpose, but I wouldn't go below pH 7.8. Definitely target pH below pH 8.5, even at the end of the light cycle.
2. Add high pH additives (limewater/kalkwasser and high pH two-part calcium and alkalinity additive systems, especially) so that they mix quickly and do not enter pumps or pass over heaters before mixing in well. Add them at times of the day when low pH conditions exist (usually early morning). Reduce these types of additives, if necessary.
3. Reduce the alkalinity. The lower the better for this purpose, but I would not target levels below 2.5 meq/L (7 dKH). Definitely target alkalinity below 4 meq/L (11 dKH).
4. Reduce the calcium level. The lower the better for this purpose, but I would not target the calcium below 380ppm. Definitely target the calcium below 500 ppm.
5. Maintain an appropriate magnesium level of 1250 -1350 ppm. Higher levels (up to, say, 1500 ppm) will help reduce precipitation further, and some aquarists have resorted to this, but I do not know at what level magnesium becomes toxic.
6. If you use an iron-based phosphate binder, either situate it well upstream of pumps and heaters or discontinue its use. Chelated iron supplements (added to supply macroalgae with iron) are not as likely, in my opinion, to cause precipitation, but may still contribute to some degree.
7. Use pumps that do not get as hot internally (external heat is not the concern here). I do not, however, have specific advice on which pumps would be best in this regard. Plastic impellers, while wonderful from a chemical resistance standpoint, are poor heat conductors, so the heat that comes from pushing against the water is not as rapidly dissipated as it would be by impellers made from other materials.
8. Elevated phosphate and organics can reduce calcium carbonate precipitation. While I do not recommend intentionally raising these for this purpose, aquarists may find that if they reduce the levels of these materials, that precipitation may become worse.
What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com
Precipitates on Heaters and Pumps
The precipitate that forms on heaters (Figure 2) and pumps is primarily calcium carbonate. Natural seawater and reef aquarium water is often supersaturated with calcium carbonate, but the precipitation is kept at a very slow pace, primarily by magnesium ions (for reasons described later in this article). Certain factors, however, push the supersaturation even higher, and the "pressure" to precipitate becomes too high for the magnesium to prevent it. These factors include elevated calcium, alkalinity, pH, and in the case of heaters and pumps, elevated temperature. How these factors impact supersaturation is detailed later in the article, but the following section summarizes the effects.
Chief among the factors causing precipitation are alkalinity and pH. While most aquarists would be unlikely to have in their aquaria double the calcium level of natural seawater (more than 800 ppm), many folks have doubled its supersaturation level via alkalinity and pH. With all other things being similar, for example, an aquarium with a pH of 8.5 has twice the supersaturation of one with a pH of 8.2, and an aquarium with a pH of 8.2 has twice the supersaturation of one with a pH of 7.9.
Alkalinity, likewise, can be a big contributor to precipitation. Many aquarists push alkalinity to elevated levels, approaching or exceeding twice the naturally occurring levels (about 2.5 meq/L, or 7 dKH). That change can, in turn, double the supersaturation.
Elevated temperature impacts calcium carbonate precipitation in two ways: 1) by simply reducing the solubility of CaCO3 (which is more soluble at lower temperatures) and 2) by causing the formation of additional carbonate from the bicarbonate in solution. These effects are roughly similar in magnitude, and are one of the reasons that pumps and heaters can be more rapidly coated with calcium carbonate precipitate than other objects in the same aquarium.
Another possible reason that pump impellers and heaters get coated more rapidly than other surfaces is that such surfaces may be less likely to become coated with a film of bacteria that prevent calcium and carbonate from reaching the surface. Heaters may become too hot for such bacterial films to form properly, and pump impellers may have enough water motion around them to wash away bacteria as soon as they begin to attach. Exactly how large such effects are, however, is not clear to me.
Low magnesium can also contribute to precipitation because magnesium interferes with the precipitation of calcium ions. Normally, magnesium ions slip into spots where calcium would otherwise bind, altering the surface's structure so that it no longer is a good seed crystal for further calcium carbonate precipitation. Fewer magnesium ions in solution makes this process less effective.
Finally, it appears that ferric ion (Fe+++) may help initiate the precipitation of calcium carbonate. Such ions may be added directly in some products, and can be released from iron-based phosphate binders such as Rowaphos, Phosban, and Phosphate Killer.
Preventing Precipitates on Heaters and Pumps
While the calcium carbonate that precipitates onto heaters and pumps can be readily removed by soaking them in acid (undiluted vinegar or diluted muriatic acid/hydrochloric acid: 1 part acid added to 9 parts fresh water), it is often easier to prevent the buildup in the first place. The following actions can be taken if the aquarium has excessive precipitation of calcium carbonate:
Note: actions 1, 3, and 4 may also make it harder for calcifying organisms such as corals and coralline algae to calcify, so they may grow more slowly if a significant reduction is made in pH, calcium or alkalinity.
1. Reduce the overall pH. The lower the better for this purpose, but I wouldn't go below pH 7.8. Definitely target pH below pH 8.5, even at the end of the light cycle.
2. Add high pH additives (limewater/kalkwasser and high pH two-part calcium and alkalinity additive systems, especially) so that they mix quickly and do not enter pumps or pass over heaters before mixing in well. Add them at times of the day when low pH conditions exist (usually early morning). Reduce these types of additives, if necessary.
3. Reduce the alkalinity. The lower the better for this purpose, but I would not target levels below 2.5 meq/L (7 dKH). Definitely target alkalinity below 4 meq/L (11 dKH).
4. Reduce the calcium level. The lower the better for this purpose, but I would not target the calcium below 380ppm. Definitely target the calcium below 500 ppm.
5. Maintain an appropriate magnesium level of 1250 -1350 ppm. Higher levels (up to, say, 1500 ppm) will help reduce precipitation further, and some aquarists have resorted to this, but I do not know at what level magnesium becomes toxic.
6. If you use an iron-based phosphate binder, either situate it well upstream of pumps and heaters or discontinue its use. Chelated iron supplements (added to supply macroalgae with iron) are not as likely, in my opinion, to cause precipitation, but may still contribute to some degree.
7. Use pumps that do not get as hot internally (external heat is not the concern here). I do not, however, have specific advice on which pumps would be best in this regard. Plastic impellers, while wonderful from a chemical resistance standpoint, are poor heat conductors, so the heat that comes from pushing against the water is not as rapidly dissipated as it would be by impellers made from other materials.
8. Elevated phosphate and organics can reduce calcium carbonate precipitation. While I do not recommend intentionally raising these for this purpose, aquarists may find that if they reduce the levels of these materials, that precipitation may become worse.
