Randy Question about "remote" testing of water samples

[dhoch]

Randy,

Our reef club is going to try to put together a testing/calibration table for our meetings (for testing tank water, RO/DI water, and calibrating probes, etc)

I was wondering what if any parameters would be affected by water being transported ~1-2 hours before being tested out of the following:

pH (this is the one I'm most suspicous of)
ORP
Nitrate
Phosphate
Calcium
Alkalinity
Copper
Salinity/Conductivity
Magnesium

Any suggestions on how best to transport the water (sealed, unsealed, no exposure to light etc) and how that might affect readings?

Thanks,

Dave

 

[Randy Holmes-Farley]

pH likely is a problem. Even in a totally sealed container, bacterial processes may serve to lower pH. I'm not sure I'd bother, or if I did, I'd be skeptical.

ORP may also change, even in a sealed container, as bacteria use up O2.

All of the others are likely OK as long as it is not stored so long that some sort of precipitation takes place.

 

[dhoch]

Thanks,

I'll do some ORP/Ph tests tonight and see what I can find out about degredation of those parameters.

Dave

 

[Randy Holmes-Farley]

Great. Let us know what you find.

 

[dhoch]

Well it took me a little longer than the next night (really today), but here are my results...

Just a couple of points of summary in my findings:

1) pH swing did not seem a big issue if using temporature correction (i.e. most of the pH swing happens rapidly, first 5-10 mins, then doesn't change much except for the change in the temperature)

2) ORP readings seemed to drop of quickly to what I will call steady state (but my orp starting point was low because I had just done a water change... I want to do this again starting from a much higher ORP reading... may even use my ozone reactor to artificially bring it up higher).

3) Surroundings that the water is kept in have a big affect (i.e. sunlight)...

Ok methodology:

I let my meter stabelize in my tank (A Hanna pH/temp/ORP meter) I then took about 2 cups of water from my tank and placed the meter in there and took readings ~ every 5 minutes.

Ok.... now for the actuall experiements... I did 3 and let 2 and 3 run for 3 hours... planned to do that with 1 as well, but I knocked over my sample cup before I got to 3 hours:

Note pH is a "temperature" adjusted pH (which is what my meter gives me)... I unadjusted the pH (as would happen if I used a standard probe).

Experiment 1

Elapsed 
Time 	  	pH
(min)	pH	adjust	ORP	Temp F	Temp C
0	8.03	8.04	225	76.5	24.7
6	8.04	8.08	211	74.7	23.7
11	8.05	8.12	212	72.9	22.7
16	8.06	8.15	213	71.6	22.0
23	8.08	8.20	214	70.0	21.1
26	8.09	8.22	214	69.3	20.7
31	8.09	8.23	215	68.4	20.2
36	8.10	8.26	216	67.5	19.7
41	8.11	8.28	216	66.7	19.3
46	8.11	8.29	217	66.0	18.9
56	8.12	8.32	216	64.8	18.2
74	8.12	8.35	214	63.4	17.4

Experiment 2

Elapsed 
Time 	  	pH
(min)	pH	adjust	ORP	Temp F	Temp C
0	7.91	7.96	239	73.9	23.3
5	7.95	8.00	227	74.2	23.4
10	7.95	8.02	223	73.1	22.8
15	7.96	8.04	222	72.3	22.4
20	7.96	8.05	222	71.4	21.9
25	7.97	8.08	221	70.6	21.4
30	7.98	8.10	221	70.0	21.1
35	7.98	8.11	221	69.5	20.8
40	7.98	8.12	221	68.8	20.4
45	7.99	8.14	221	68.3	20.2
50	8.00	8.15	220	68.0	20.0
55	8.00	8.16	220	67.6	19.8
60	8.00	8.17	220	67.1	19.5
65	8.00	8.17	219	66.9	19.4
70	8.00	8.17	219	66.6	19.2
75	8.00	8.18	219	66.4	19.1
80	8.01	8.19	216	66.2	19.0
85	8.01	8.19	216	66.1	18.9
90	8.01	8.19	214	66.0	18.9
95	8.01	8.20	214	65.9	18.8
100	8.01	8.20	213	65.9	18.8
105	8.01	8.20	213	65.8	18.8
110	8.01	8.20	213	65.8	18.8
115	8.01	8.20	212	65.7	18.7
120	8.01	8.20	212	65.7	18.7
125	8.01	8.20	213	65.6	18.7
130	8.01	8.20	214	65.6	18.7
135	8.01	8.20	214	65.7	18.7
140	8.01	8.20	212	65.7	18.7
145	8.01	8.20	212	65.7	18.7
150	8.01	8.20	211	65.7	18.7
155	8.01	8.20	210	65.7	18.7
160	8.01	8.20	211	65.7	18.7
165	8.01	8.20	212	65.7	18.7
170	8.01	8.20	213	65.9	18.8
175	8.00	8.19	213	65.9	18.8
180	8.00	8.18	212	66.0	18.9

Experiment 3

Elapsed 
Time 	  	pH
(min)	pH	adjust	ORP	Temp F	Temp C
5	8.00	7.97	220	78.7	25.9
10	8.02	8.02	219	76.8	24.9
15	8.03	8.05	219	75.7	24.3
20	8.03	8.07	218	74.5	23.6
25	8.04	8.09	217	73.8	23.2
30	8.04	8.10	216	73.2	22.9
35	8.04	8.11	216	72.7	22.6
40	8.04	8.12	214	72.1	22.3
45	8.05	8.14	216	71.8	22.1
50	8.05	8.15	212	71.1	21.7
55	8.05	8.15	214	70.9	21.6
61	8.05	8.16	215	70.6	21.4
65	8.05	8.16	216	70.5	21.4
70	8.05	8.16	216	70.3	21.3
80	8.05	8.17	216	70.0	21.1
85	8.05	8.17	216	69.8	21.0
91	8.05	8.17	214	69.7	20.9
96	8.05	8.18	214	69.5	20.8
101	8.07	8.19	213	69.9	21.1 (note sun started to shine on it)
106	8.05	8.17	213	69.7	20.9
110	8.05	8.17	213	69.8	21.0
115	8.05	8.17	213	69.8	21.0
120	8.05	8.17	214	69.9	21.1
125	8.05	8.17	214	69.9	21.1
131	8.05	8.17	214	70.0	21.1
136	8.05	8.17	212	70.0	21.1
141	8.05	8.17	213	70.0	21.1
145	8.05	8.17	213	70.0	21.1
150	8.05	8.17	212	70.0	21.1
155	8.05	8.17	213	69.9	21.1
161	8.05	8.17	213	69.8	21.0
165	8.05	8.17	212	69.8	21.0
170	8.05	8.17	211	69.7	20.9
175	8.05	8.18	211	69.5	20.8
180	8.05	8.18	211	69.5	20.8

Dave

 

[dhoch]

Here are there graphs from the experiments:
Experiment 1:

Experiment 2:

Experimetn 3:

Dave

 

[Randy Holmes-Farley]

Interesting results. Thanks for posting them!