Question 1

What is GH and how do you convert it?

Accepted Answer

GH (General Hardness) measures calcium and magnesium concentration. 1 °dGH = 17.848 ppm CaCO₃ = 1.786 °fH (French degrees) = 0.1783 mmol/L.

Question 2

How do you calculate CO₂ in an aquarium?

Accepted Answer

CO₂ is calculated using the Henderson-Hasselbalch equation: CO₂ (mg/L) = 3.0 × KH × 10^(7.00 - pH). The ideal range for plants is 15–30 mg/L; never exceed 30 mg/L for fish safety.

Question 3

What salinity is needed for a marine aquarium?

Accepted Answer

The ideal salinity for a marine aquarium is 35 ppt (parts per thousand), corresponding to a density of approximately 1.025 g/cm³ and a specific gravity (SG) of 1.025 at 25°C.

KH \ pH	6.0	6.4	6.6	6.8	7.0	7.2	7.4	7.6
2	60	24	15	10	6	4	2	2
4	120	48	30	19	12	8	5	3
6	180	72	45	29	18	11	7	5
8	240	96	60	38	24	15	10	6
10	300	119	75	48	30	19	12	8
12	360	143	90	57	36	23	14	9
15	450	179	113	71	45	28	18	11

Water chemistry

GH hardness conversion

KH / TAC conversion

Dissolved CO₂ calculator

Water mixing

Density & salinity (marine)

Scientific references

KH \ pH	6.0	6.4	6.6	6.8	7.0	7.2	7.4	7.6
2	60	24	15	10	6	4	2	2
4	120	48	30	19	12	8	5	3
6	180	72	45	29	18	11	7	5
8	240	96	60	38	24	15	10	6
10	300	119	75	48	30	19	12	8
12	360	143	90	57	36	23	14	9
15	450	179	113	71	45	28	18	11

KH \ pH	6.0	6.4	6.6	6.8	7.0	7.2	7.4	7.6
2	60	24	15	10	6	4	2	2
4	120	48	30	19	12	8	5	3
6	180	72	45	29	18	11	7	5
8	240	96	60	38	24	15	10	6
10	300	119	75	48	30	19	12	8
12	360	143	90	57	36	23	14	9
15	450	179	113	71	45	28	18	11

KH \ pH	6.0	6.4	6.6	6.8	7.0	7.2	7.4	7.6
2	60	24	15	10	6	4	2	2
4	120	48	30	19	12	8	5	3
6	180	72	45	29	18	11	7	5
8	240	96	60	38	24	15	10	6
10	300	119	75	48	30	19	12	8
12	360	143	90	57	36	23	14	9
15	450	179	113	71	45	28	18	11