INTRODUCTION TO REEF WATER CHEMISTRY

By:

Alex B.

and

Dick O.

NITROGEN

Main forms of nitrogen we are concerned with include:

• Ammonia (NH3)• Ammonium (NH4

+)

• Nitrite (NO2-)

• Nitrate (NO3-)

NITROGEN – AMMONIA AND AMMONIUM

NITROGEN – USES AND ACCEPTABLE LEVELS

What is nitrogen used for?

• Nucleic acids

• Amino acids proteins

Acceptable levels of nitrogen

Ammonia/Ammonium – < 0.1 ppm

Nitrite – < 0.2 ppm

Nitrate – preferably < 5 pmm

NITROGEN- SOURCES AND PATHWAYS1. Fixation

• Atmospheric nitrogen 78%• Cyanobacteria can fix nitrogen!

2. Mineralization• Decomposition of uneaten fish

food• Fish excretion

3. Nitrification• Ammonium to Nitrite (aerobic)• Nitrite to Nitrate (aerobic)

4. Assimilation• Algae, bacterial, and animal

growth

5. Denitrification• Nitrate into nitrogen (anaerobic,

dissipated through gas exchange)

EXPORTING NITROGEN – CARBON DOSING

Pros:

• Relatively cheap to dose

• Low space requirement

• Can improve coloration of corals

• Also removes phosphorous

Cons:

• Requires a good protein skimmer

• Must watch alkalinity levels

• Dosing can lower pH

• Carbon may promote cyanobacteria

EXPORTING NITROGEN – COIL DENITRATOR

Pros:

• Simple design

• Takes advantage of denitrification bacteria

Cons:

• Requires time for bacteria to colonize

• Must regularly check flow through reactor for changes

• Can get clogged and requires cleaning – resets cycle

EXPORTING NITROGEN – SULFUR DENITRATOR

Pros:

• Can remove large amounts of nitrate

• Media lasts for months

Cons:

• Requires time for bacteria to colonize

• Can lower pH

• Must still maintain water changes to remove sulfates

• Too slow of an effluent rate may release hydrogen sulfide

EXPORTING NITROGEN – MACRO ALGAE

Pros:

• Can help stabilize pH with reversed lighting schedule

• Provides refuge for copepods and other macro-invertebrates

• Also removes phosphorous

Cons:

• Requires regular removal of algae to export nitrogen

EXPORTING NITROGEN – DEEP SAND BED

Pros:

• Simple design

• Takes advantage of denitrification bacteria

• Does not require additional equipment *unless in a remote deep sand bed

Cons:

• Requires time for bacteria to colonize

• Large sand beds can hold lots of detritus, eventually becoming a phosphate source

• Toxic gases can be released if disturbed

EXPORTING NITROGEN – ZEOLITIC MEDIA

Pros:

• Attracts nitrogen ions (NH4+ )

• Can also take advantage of bacteria

• Can create a very low nutrient system

Cons:

• Requires regular dosing of additives

• Media has high affinity for other cations (Ca2+, K+, Mg2+)

EXPORTING NITROGEN – POLYMERS AND SPONGES

Pros:

• Quick acting in case of disasters

• Can absorb both organic and

ionic forms of nitrogen (NH4+

)

(Poly-Filter)

• Some products can be recharged (Purigen)

Cons:

• Media may need replaced frequently depending on bioload

• Purigen only removes organic nitrogen

PHOSPHOROUS

Main forms of ionic phosphorous we are concerned with include:

• Hydrogen phosphate (HPO42-) 79%

• Phosphate (PO43-) 20%

• Dihydrogen phosphate (H2PO4-) 1%

PHOSPHOROUS – USES AND ACCEPTABLE LEVELS

What is phosphorous used for?

• Adenosine Triphosphate (ATP) and other organic compounds

• Phospholipids

• Bones (calcium phosphate)

Acceptable levels of phosphorous

< 0.03 ppm or as low as possible

PHOSPHOROUS – SOURCES AND PATHWAYS

1. Mineralization• Decomposition of uneaten fish

food2. Assimilation

• Algae, bacterial, and animal growth

3. Sorption• Binding of inorganic

phosphorous (Fe, Al, Mn oxides; clays and detritus)

4. Desorption• Release of inorganic phosphate

5. Precipitation• Phosphate falling out of solution

6. Dissolution• Dissolving of soluble phosphate

or introduction via input water (top-off or water change water)

EXPORTING PHOSPHOROUS – OXIDES

Pros:

• Quick acting and highly absorbent

• Some reports of recharging GFO

• May bind some organic phosphate

Cons:

• Media may need replaced frequently depending on feeding

• Some reports of aluminum oxide causing problems with corals

• Can clump up from calcium precipitation

EXPORTING PHOSPHOROUS – BIOLOGICAL CONTROL

Pros:

• Can be relatively inexpensive

• Allows algae and bacteria to do the work for you

Cons:

• Not as quick to export phosphate as other methods

• If using a pro-biotic system, a good protein skimmer is required

• Biota can only consume phosphate if nitrogen is present (Redfield stoichiometry)

Carbon : Nitrogen : Phosphorous 106 : 16 : 1

EXPORTING PHOSPHOROUS – PRECIPITATION

Pros:

• Immediately reacts with phosphorous

• Large amounts of phosphorous can be removed through precipitation

Cons:

• Requires a fine filter removal (5 µm)

• May precipitate carbonates if no phosphate is available

TEMPERATURE

• Appropriate temperature range: 76° F - 81° F (24 – 27°C)

• Lower temperatures can hold more dissolved oxygen

• Higher temperatures can facilitate coral bleaching

PH SALINITY• pH should range from 8.1 - 8.3

• Major source of pH issues is CO2

CO2 + H2O H2CO3

Ways to cure low pH issues:

• Proper aeration can alleviate seasonal low pH issues

• Use an aragonite based substrate

• Dosing calcium hydroxide (kalkwasser)

• Scrubbing the air of CO2 with soda

lime can help with most extreme pH issues

• Appropriate salinity can range from 1.025 to 1.027sg (34-36 ppt)

• Consistency of the desired salinity is most important

• For best results use a calibrated refractometer with an accurate auto top off system.

CALCIUM – USES AND ACCEPTABLE LEVELS

• Main form of calcium we are concerned with: Ca2+

• Calcium is a component of coral skeletons (calcium carbonate) and fish skeletons (calcium phosphate)

• Appropriate calcium range: 380-450 ppm, stability is most important

DOSING CALCIUM – CALCIUM REACTOR

Pros:

• Cheap media lasts for months

• Doses calcium and alkalinity in appropriate proportions

• Can accommodate big systems with large calcium demands

Cons:

• Larger start up cost

• Small adjustments of effluent flow rate may be needed periodically

• Complexity

DOSING CALCIUM – CALCIUM CHLORIDE SOLUTION

Pros:

• Accurate and independent dosing can maintain very consistent results

• Can easily adjust water (tank or water change water) using reef calculators

• Some brands contain other important trace elements (B-Ionic)

Cons:

• Chemicals may become expensive over time with higher calcium demand

• Daily dosing is required for best results

• Will raise salinity over time

DOSING CALCIUM – CALCIUM HYDROXIDE SOLUTIONPros:

• Can assist in keeping pH within desirable ranges

• Also increases alkalinity

• Good for maintaining consistency

• Low start up costs, cheap to maintain

Cons:

• Very alkaline (pH of 12.4) solution can raise pH too fast with quick additions

• Must be dosed in a high flow area to reduce precipitation

• Not ideal for raising calcium by large amounts

• Limited by evaporation

ALKALINITY – USES AND ACCEPTABLE LEVELS

Main forms of alkalinity we are concerned with:

• Carbonate (CO32-)

• Bicarbonate (HCO3-)

• Alkalinity is a component of coral skeleton and helps buffer the water

• Appropriate alkalinity range: 7-11 dKH, stability is most important

DOSING ALKALINITY – CALCIUM REACTOR

Pros:

• Cheap media lasts for months

• Doses calcium and alkalinity in appropriate proportions

• Can accommodate big systems with large calcium demands

Cons:

• Larger start up cost

• Small adjustments of effluent flow rate may be needed periodically

• Complexity

DOSING ALKALINITY – SODIUM BICARBONATE SOLUTION (BAKING SODA)

Pros:

• Accurate and independent dosing can maintain very consistent results

• Can easily adjust water (tank or water change water) using reef calculators

• Most common form of alkalinity in sea water

Cons:

• Chemicals may become expensive over time with higher calcium demand

• Daily dosing is required for best results

• Slight pH lowering effect upon initial dose

DOSING ALKALINITY – SODIUM CARBONATE SOLUTION (SODA ASH)

Pros:

• Accurate and independent dosing can maintain very consistent results

• Can easily adjust water (tank or water change water) using reef calculators

• Helps maintain high pH

Cons:

• Chemicals may become expensive over time with higher calcium demand

• Daily dosing is required for best results

DOSING ALKALINITY – CALCIUM HYDROXIDE SOLUTIONPros:

• Can assist in keeping pH within desirable ranges

• Also increases calcium

• Good for maintaining consistency

• Low start up costs, cheap to maintain

Cons:

• Very alkaline (pH of 12.4) solution can raise pH too fast with quick additions

• Must be dosed in a high flow area to reduce precipitation

• Not ideal for raising alkalinity by large amounts

• Limited by evaporation

MAGNESIUM – USES AND ACCEPTABLE LEVELS

• Main form of magnesium we are concerned with: Mg2+

• Magnesium helps balance calcium and alkalinity by allowing both to co-exist without excessive precipitation

• Magnesium is used in the building of the corals skeleton

• Appropriate magnesium range: 1200-1400 ppm, or 3x your calcium level

Table 1. Magnesium in calcium carbonate skeletons

Organisms

Magnesium content of skeleton (weight %)

Faviid 0.07 - 0.36%

Fungia 0.095-1.22%

Tubiporidae 2.98-3.52%

Porites 0.095-1.22%

Pocillopora 0.34%

Dendrophyllia 0.05%

Coralline algae: Lithophyllum and Lithotamnium

2.0-2.8%

benthic marine Ostracoda (crustaceans)

0.5-1.3%

DOSING MAGNESIUM – CALCIUM MAGNESIUM CARBONATE (DOLOMITE)

Pros:

• Media lasts for months

• Doses magnesium, calcium, and alkalinity

• Can accommodate big systems with large magnesium demands

Cons:

• Must be used in a calcium reactor (larger start up cost)

DOSING MAGNESIUM – MAGNESIUM CHLORIDE AND MAGNESIUM SULFATE

• For best results use a mixture of both with ratios depending on current dosing regime

Pros:

• Accurate and independent dosing can maintain very consistent results

• Can easily adjust water (tank or water change water) using reef calculators

Cons:

• Chemicals may become expensive over time

• Calcium Reactor

• Kalkwasser

• Two-part systems

HELPFUL TIPS AND LINKS

• Reef Chemistry Calculator: http://reef.diesyst.com/chemcalc/chemcalc.html

• DIY Two-part recipes: http://www.reefkeeping.com/issues/2006-02/rhf/

• Remember to always use reverse osmosis de-ionized water!

• Common misunderstanding is 2-part “must” be dosed in equal proportions

REEF PARAMETERSTable 1.  Parameters critical to control in

reef aquaria.

Parameter:Reef Aquaria

Recommendation:Calcium 380-450 ppm

Alkalinity

2.5-4 meq/L7-11 dKH

125-200 ppm CaCO3 equivalents

Salinity35 ppt

sg = 1.026Temperature 76-81° F

pH7.8-8.5 OK

8.1-8.3 is betterMagnesium 1200-1400 ppmPhosphate < 0.03 ppmAmmonia <0.1 ppm

Table 2.  Other parameters in reef aquaria.

Parameter:Reef Aquaria

Recommendation:

Silica < 2 ppm, much lower if diatoms are a problem

Iodine Control not recommended

Nitrate < 5 ppm

Nitrite < 0.2 ppm typically

Strontium 5-15 ppm

ORP Control not recommended

Boron < 10 ppm

Iron Below Kit Detection Limits (additions OK)

QUESTIONS?