1	Water Chemistry
2	Salinity What is it? How is it measured? Specific Gravity Hydrometers Refractometer Conductivity Probes Test Kit Temperature Considerations
3	Ionic Speciation Na: 10,810 ppm Cl: 19,470 ppm Mg: 1,272 SO₄: 2,688 Ca: 412 BO₄: 25 K: 398 CO₃: 114 Sr: 8 Total = 35,198 ppm or 35.2 ppt or 1.026 sg
4	pH What is pH? pH = -log[H⁺] H⁺ = H₃O⁺ Logrithmic scale Why does it matter? NSW: 8.2 (average) Safe range: 7.8 – 8.5
5	Alkalinity What is alkalinity? Amount of acid (H⁺) needed to lower the pH to 4.2 (carbonate equivalency point) What ions contribute to alkalinity? TA = [HCO₃^-] + 2[CO₃^--] + [B(OH)₄^-] + [OH^-] + [Si(OH)₃O^-] + [MgOH⁺] + [HPO₄^--] + 2[PO₄^--] – [H⁺]
6	Measuring Alkalinity Test kits measure Total Alkalinity by a single acid/base titration Units of Alkalinity ppm CaCO₃ dKH meq/l 1 meq/l = 2.8 dKH = 50 ppm CaCO₃
7	Contribution to Alkalinity HCO₃^- 89.8% CO₃^-- 6.7% B(OH)₄^- 2.9% Si(OH)₃O^- 0.2% MgOH⁺ 0.1% OH^- 0.1% PO₄^-- 0.1%
8	Carbonate Alkalinity CA = [HCO₃^-] + 2[CO₃^--] (96.5+ % of TA) CO₂ + H₂O = H⁺ + HCO₃^- = 2H⁺ + CO₃^-- Sources of CO₂ Atmosphere Respiration
9	Carbonate Additives Does it matter what “type” is added? HCO₃^- will equilibrate to CO₃^-- and CO₂ CO₃^-- will equilibrate to HCO₃^- and consume CO₂ OH^- will equilibrate to CO₃^--, HCO₃^- by consuming CO₂
10
11	Some Solutions to pH Problems Low pH: Caused by CaCO₃/CO₂ reactor: Two stage reactor may help, increased aeration, use kalkwasser for make-up water. Caused by high atmospheric CO₂ levels: Open a window or “pipe” outside air into skimmer or sump. Caused by low alkalinity: Add carbonates to increase system alkalinity. Proper gas exchange is critical!
12	Some Solutions to pH Problems High pH: Caused by kalkwasser additions: Use other alkalinity additives in addition to (or in place of) kalkwasser such as CaCO₃/CO₂ reactor or B-ionic. Add vinegar to the kalkwasser solution. Caused by other additive: Reconsider the use of this additive. Water changes are quick short-term solutions to any pH problem.
13	Sea Water Buffering HCO₃^- = CO₃^-- + H⁺ pKa=8.9 B(OH)₃ + H₂O = B(OH)₄^- + H⁺pKa=8.5 Buffering Capacity, β = meq/l/pH β = 2.303 Cα_oα₁ = Δ[H⁺] / ΔpH
14	Sea Water Buffering HCO₃^- + OH^- = CO₃^-- + H₂O CO₃^-- + H⁺ = HCO₃^- This “system” effectively consumes both H⁺ and OH^-. It resists pH changes in both directions.
15	Alkalinity vs. Buffering Alk Buffer CO₃: 96.5% 77% BO₄: 2.9% 23% pH=8.5 is 40% more buffered then pH=8.2 pH=7.8 is 50% less buffered then pH=8.2 (all at the same alkalinity)
16	pH Stability Increase aeration Use kalkwasser only at night Use CaCO₃/CO₂ reactors only at day Use a reverse daylight refugium Increase carbonate alkalinity Increase boron level
17	Alkalinity and pH Relationship between alkalinity and pH: A_c=k₁k_Hp_CO2/[H⁺] + 2k₁k₂k_Hp_CO2/[H⁺]² pH=-log[H⁺] Equilibrium CO₂ concentration in water is only dependent on atmospheric CO₂ levels and water temperature. pH does not matter!
18
19	Why Doesn’t My Tank Do That Equilibrium vs. Kinetics: role of gas/water interfacial area CO₂ Consumers: Photosynthetic Animals CO₂ Producers: Animal respiration, Reactors High atmospheric CO₂ levels
20	Calcium NSW: 410 ppm Exists almost exclusively as calcium ion, some may be chelated to certain organic molecules. Ca⁺⁺ + CO₃^-- = CaCO₃ K_sp = [Ca][CO₃] K_sp > [Ca][CO₃] (undersaturated) K_sp < [Ca][CO₃] (supersaturated)
21	CaCO₃ Saturation Ω is defined as the degree of calcium carbonate saturation. If Ω=1 CaCO₃ is at equilibrium. If Ω<1, CaCO₃ will dissolve. If Ω>1 CaCO₃ will precipitate. Ω = [Ca][CO₃]/k_sp Ω_nsw= 3
22	Why Doesn’t It Precipitate? Kinetics vs. Equilibrium Ion pairing between Ca & SO₄ & HCO₃ Ion pairing between Mg and CO₃ Mg ions “poison” growing CaCO₃ crystals Organics can “poison” growing crystals Because of this CaCO₃ is 25X more soluble in seawater then freshwater!
23	Temperature Effects CaCO₃ is more soluble at lower temperatures. Most likely spot in our tanks for precipitation is where it’s hot (heaters and pumps).
24	But My Sand Appears to Dissolve Where can CaCO3 dissolve? Places where the pH is “low”: Within a deep sand bed Interstitial areas within live rock Places or times when alk gets very low
25	Choosing an Alk/Ca Additive What ranges are acceptable: Alkalinity: 2.5 – 4 meq/l Calcium: 370 – 450 ppm If tank has chronic low pH, it’s safer to push the levels even higher.
26	Choosing an Alk/Ca Additive Balanced vs. Unbalanced 20 ppm Ca per 1 meq/l Carbonate Sources of Unbalanced additives: Baking Soda: NaHCO₃ Washing Soda: Na₂CO₃ Commercial Buffers: mix of carbonate/borate Turbo Calcium: CaCl₂
27	Effects of Unbalance Additives
28	Choosing an Alk/Ca Additive When to use unbalanced additives: To make adjustments to either Calcium or Alkalinity separately. If you don’t care about having an ionic imbalance in your reef tank.
29	Choosing an Alk/Ca Additive Sources of balanced additives: Kalkwasser CaCO3/CO2 reactor CaCO3 without CO2 Calcium Acetate (All in One) One part inorganic salt mixes (Biocalcium) 2 part salt mixes (B-ionic, C-balance) Water changes Think of them as alkalinity maintanance not calcium!
30	Choosing an Alk/Ca Additive Kalkwasser Ca(OH)₂ = Ca⁺⁺ + 2OH^- OH^-+ CO₂ = HCO₃^- OH^-+ HCO₃ = CO₃^— Vinegar (acetic acid) can be mixed with the kalkwasser to both increase the potency and decrease the pH. Cheap food grade lime (pickling lime).
31	Choosing an Alk/Ca Additive Kalkwasser (continued) Pros Very inexpensive start-up costs Can be very inexpensive to use (Ball brand) Raises pH Can help to remove heavy metals and phosphate Does not effect salinity Cons Limited to evaporation rate Raises pH (easy to overdose) Cost: $0.10 – $1.10 per 1000 meq
32	Choosing an Alk/Ca Additive CaCO3/CO2 Reactor CO₂ +H₂O = H⁺ + HCO₃^- CaCO₃ + H⁺ = Ca⁺⁺ + HCO₃^- ------------------------------------------------------------- CO₂ + H₂O + CaCO₃ = Ca⁺⁺ + 2HCO3^- Lower Ω below 1, dissolve CaCO₃, then dump back into tank and degass excess CO₂.
33	Choosing an Alk/Ca Additive CaCO3/CO2 Reactor (continued) Pros Can add an almost unlimited amount of Ca/CO3 Cheap to maintain Very hard to overdose Does not effect salinity Cons Large start-up cost Many tanks have low pH Everything in media dissolves (P, Copper, ect) Cost: $0.35 per 1000 meq
34	Choosing an Alk/Ca Additive CaCO₃ without CO₂ CaCO₃ = Ca⁺⁺ + CO₃^-- Could be mixed with fresh make-up water (ca. 30 ppm Ca, 25x less potent then kalkwasser). Media in tank water.
35	Choosing an Alk/Ca Additive
36	Choosing an Alk/Ca Additive CaCO₃ without CO₂(continued) Pros Cheap to start-up and use Can not overdose Does not effect pH Does not effect salinity Cons Very limited (NSL tapwater: 100 ppm Ca, 4 meq/l) Cost: $0.008 per 1000 meq
37	Choosing an Alk/Ca Additive Calcium acetate Ca(CH₃COO^-)₂ = Ca⁺⁺ + 2CH₃COO^- CH₃COO^- + 2O₂ = HCO₃ + CO₂ + H₂O Can also help in denitrification 5CH₃COO^- + 8NO₃^- = 10CO₂ + 4N₂ + 13OH^- +H₂0 Very similar to vinegar and kalkwasser
38	Choosing an Alk/Ca Additive Calcium acetate (continue) Pros Use only limited by tank metabolism Very cheap start-up cost Does not effect pH Does not effect salinity Cons Expensive for a high demand tank Acetate confounds alkalinity test kits Cost: $10 per 1000 meq
39	Choosing an Alk/Ca Additive 1 part salt mix NaHCO₃, CaCl₂, and residual salt Must be sprinkled into tank water directly. Can cause burning if solids fall on coral.
40	Choosing an Alk/Ca Additive 1 part salt mix Pros Very cheap start-up cost Unlimited usage Does not impact pH Cons Expensive for high demand tanks Raises salinity Must be kept dry Cost: $4.50 per 1000 meq
41	Choosing an Alk/Ca Additive 2 part salt mix (B-ionic) Essentially a salt mix with elevated calcium and alkalinity.
42	Choosing an Alk/Ca Additive 2 part salt mix (B-ionic) (continued) Pros No start-up cost Very little pH impact Very hard to overdose Easy to use Cons Expensive in a high demand tank Increases salinity Cost: $8.90 per 1000 meq
43	Choosing an Alk/Ca Additive Water Changes Pros No start-up cost No pH impact No salinity impact Can’t overdose Cons Limited to a low-medium demand tank Cost: $30 per 1000 meq
44	Ca/Alk Addition Philosophy
45	Magnesium NSW: 1280 ppm Why is it important? Ion pairing allows for high calcium/alkalinity levels Poisons CaCO₃ crystal formation Where does it go? Co-precipitation with calcium Coralline algae
46	Magnesium Homemade additives: Epsom salts, MgSO₄ MgCl₂
47	Boron NSW: 5 ppm Exists as: B(OH)₃ boric acid B(OH)₄^-borate ion Pound for pound it’s a better buffer then carbonates
48	Boron How is it used? Co-precipitation with CaCO3 (coral skeletons contain 50 – 100 ppm B) Algae uptake Where does it come from? Food Comercial buffers Other additives
49	Boron Is there anything wrong with elevated boron levels? Toxic to some marine life (28 – 74 ppm) Confounds alkalinity test kits Some salt mixes contain elevated boron Homemade additive: Borax (21.5% Boron)
50	Iodine Naturally exists as: I^- iodide (0.01 – 0.02 ppm) IO₃^- iodate (0.04 – 0.06 ppm) Organic Iodine such as methyl iodide What uses it? Corals (gorgonia, “black corals”, soft corals) Trunicates, sponges, worms, shrimp Algae
51	Iodine Toxicity? I₂ is a bactericide, I^- and IO₃^- are essentially safe. Lugols solution contains I₂ and I^- What type is used? Most prefer I^-, but can use IO₃^-
52	Iodine Sources of Iodine: Food Supplements (KI, KIO₃, Lugols, ect) Test kits: Seachem only detects I^- and I₂ (if present) Most others detects I^-, IO₃^- and I₂ In general hobby kits are difficult to use and interpret results
53	Phosphorus Exists as: Orthophosphate, PO₄^-- Polyphosphate, P-O-P Organic, DNA, ATP, other proteins Why does it matter? Can lead to excessive algae growth Inhibits calcification
54	Phosphorus NSW: 0.005 ppm At 0.03 ppm it becomes limiting to many species of phytoplankton. Where does it come from? Food Make-up water Test kits only measure orthophosphates
55	Phosphorus How to export: Macro algae export Precipitation of Ca₃(PO₄)₂ in high pH areas such as where kalkwasser is dripped. Precipitation of Ca₃(PO₄)₂ on surface of liverock/substrate. Can lead to long term algae problems Adsorption (only works on orthophosphates) Skimming (only works on organic phosphates)
56	Silica Exists naturally as: Si(OH)₄ silicic acid Si(OH)₃O^- silicate Why is it needed? Diatoms Sponges Mollusks (teeth)
57	Silica Where does it come from? Tapwater Food Kalkwasser The ocean is actually undersaturated in SiO₂, meaning the quartz sand beaches are dissolving… but the kinetics are VERY slow. Can dose “water glass”, NaSi(OH)₃O^-
58	Iron Needed/wanted by most algaes Grow greener and faster, may help macro out compete micro Good source of electrons for biological redox reactions (photosynthesis) Fe⁺⁺ = e^- + Fe⁺⁺⁺ Look for an additive that is Fe⁺⁺ with a mild chelate such as citrate or EDTA.