Calcium reactor question

[21chip]

Will the PH Lower it self using a reactor or will it maintain the PH level in the main tank? Does all the low ph in the reactor stay in the reactor?

 

[Randy Holmes-Farley]

The pH of a reef aqaurium generally drops a bit when using a CaCO3/CO2 reactor because it necessarily delivers extra CO2 to the water.

 

[21chip]

I always thought it only did calcium. I was looking at a GEO 618. I have always been old school with adding dry cal. and alk. Just that there is a lot of thing getting bigger, and using it up in less then a week. its hard to keep up with it.

 

[Randy Holmes-Farley]

I always thought it only did calcium. I was looking at a GEO 618. I have always been old school with adding dry cal. and alk. Just that there is a lot of thing getting bigger, and using it up in less then a week. its hard to keep up with it.

CaCO3/CO2 reactors add both calcium and alkalinity.

Here's a section from an upcoming article:

Calcium Carbonate/Carbon Dioxide Reactors

Calcium carbonate/carbon dioxide reactors work by removing water from the tank, adding carbon dioxide to reduce the pH to about pH 6.5, and then allowing the more acidic water to dissolve solid calcium carbonate media that is present in a mixing chamber. The water is then returned to the tank with its extra calcium and alkalinity (bicarbonate):

CaCO₃ + H⁺ → Ca₂⁺ + HCO₃^-

Reef tanks employing such reactors typically run at a pH below that of natural seawater, with typical tank pH values of 7.7 to 8.1. The reason for the low pH is the constant delivery of low pH solution to the tank, adding both excess CO₂ and bicarbonate. There is no way around this completely, but some reactors incorporate a second chamber, allowing the liquid to pass over additional calcium carbonate media, making better use of the carbon dioxide that is actually added. Aquaria then blow off this extra CO₂ and the pH rises, but the effect is typically not complete, and the pH often stays below what would be the case if the same tank water were fully aerated (that is, equilibrated) with normal air.

The media used is important in these systems, with the aragonite form of calcium carbonate being more readily dissolved than the calcite form (although both work). Also, the nature of the impurities can be very important, as nearly all of the impurities will be dissolved and delivered to the tank. Some of these impurities may be desired by the aquarist (such as magnesium and strontium) and some may not be (such as phosphate or copper). Phosphate in reactor media has sometimes become a point of competition between commercial suppliers of media for such reactors, but I would advise aquarists to be skeptical of some of these claims.

One big advantage of these reactors is that they can be scaled to deliver any amount of calcium and alkalinity needed by any tank. For this reason, they are greatly favored by those who have tanks with a high demand for calcium and alkalinity. Because of the low pH that often results, many of these aquarists choose to dose limewater in conjunction with the reactor, not because the reactor cannot supply enough calcium and alkalinity, but purely to raise the pH in the tank itself. The synergy between limewater and CaCO₃/CO₂ reactors involves more than just pH. Limewater uses up CO₂ and CaCO₃/CO₂ reactors deliver it to the tank. Together, they combine to keep CO₂ (and consequently, pH) more in line with natural seawater.

Calcium carbonate/carbon dioxide reactors take up a substantial amount of space, since one needs a carbon dioxide cylinder, a reaction chamber, and a pump. Typically, these systems are used close to a tank, but they could be remote if appropriate water flows to and from the tank could be worked out. Once an aquarist has properly adjusted the reactor system, it requires minimal monitoring for a substantial period. Tank salinity will not increase over time using calcium carbonate/carbon dioxide reactors.

The likelihood of problems from overdosing using such a reactor is minimal. Since the pH is typically low, even substantially elevated calcium and alkalinity values may not cause a dramatic calcium carbonate precipitation event. More likely is just slow precipitation onto heaters and pump impellers. Accidental delivery of large amounts of CO₂ to the tank is a concern, but that is a rare accident.
The initial costs of such reactor systems can be considerable, typically about $300-600 for the reactor itself, plus additional costs for the CO2 apparatus. Media costs vary, but a bit over $2 per pounds is typical. That puts the media cost at about $0.30 per thousand meq of alkalinity. DIY ground limestone can be used as media for a tiny fraction of this cost, if you can find it locally. The carbon dioxide cost also needs to be figured in, so that might push the total to about $0.40 per thousand meq of alkalinity.

The primary safety concern for these systems involves the carbon dioxide gas cylinder. Any high-pressure gas cylinder can be very dangerous if the cylinder head should become damaged. So be careful to not drop such cylinders least they become rockets.

 

[Randy Holmes-Farley]

edit: oops, wrong thread.

 

[Randy Holmes-Farley]

I always thought it only did calcium. I was looking at a GEO 618. I have always been old school with adding dry cal. and alk. Just that there is a lot of thing getting bigger, and using it up in less then a week. its hard to keep up with it.

FWIW, many people dose calcium and alkalinity daily, if not more frequently. Some using dosing pumps to dose it many times per day to keep it steady, but once a day manual dosing also works for many people.

I think a better best is a liquid two part system rather than independent dosing of calcium and alkalinity.

 

[21chip]

I have use 2 part for a long time and works good but im not always there to add it. I need to make it more automated. Dose pumps scare me too with timers and all. I did not know about the lime and CO2. I will read more on that. Is there a media you can add to reactor to bring up ALK. Lime?

 

[Randy Holmes-Farley]

If you mean a reactor using seawater, the only thing you can use is a CaCO3/CO2 reactor.

Lime must be put into fresh water.