Yesterday I changed and cleaned all filters in processing loop 1L. This resulted in a big gulp water change of about 8 gallons. Half a liter of NeoMag was put into the 25 micron section. I will be watching both GH and KH very closely. The small-pore biofilter media (Matrix, Siporax, and MarinePure) was removed and rinsed out thoroughly in a hose stream. Just to be strictly correct about it, the efficiency is considered compromised until the biofilms repopulate. I will do the same in loop 1R this week. I have 20 gallons of undisturbed Coralife Bioballs in line, so no worries.
This week's trimming is overdue - i.e. last week's trimming is still not yet done - and the shade is depressing the O2 saturation cycle. Yesterday it peaked at 8.4 ppm. In itself, nothing concerning here, but it must be put right ASAP as the biofilters will need the boost.
Yesterday I cleaned and changed all filters in processing loop 1R, and high speed loops 2 and 3, with the accompanying large big gulp water change. All the small-pore biofilter media was removed and rinsed. 250 mL each of SeaChem Purigen and Continuum Catalytic Carbon were put into the 25 micron cartridge in loop 1R.
The program setting for CO2PRIMARY has allowed the running average pH to settle to 6.82. I am adjusting this just slightly to get back to 6.84.
The running average ORP has been fairly stable at > 530 mV since 1 March when a large charge of Purigen + Catalytic Carbon was installed. Reviewing the redox results over the last six months, ORP rose to > 400 mV after implementation of the streaming water change regimen, and it rose again to > 500 mV when I started using good quality pelleted activated carbon. Adding the high-grade media is a further improvement in organics scavenging efficiency.
Phosphate continues to persist without supplementation. Between plant consumption and water changes it remains within oligotrophy, seldom exceeding 1 ppm. Nitrate and iron values have been good with present plant utilization. Today I added KNO3 and micros to compensate the large water changes. After filter maintenance, I have been adding 20 ml of SeaChem Nitrogen and 10 ml of Flourish Comprehensive.
Almost certainly, the NO3 incline is due, in part, to the post-water change KNO3 boosts. However, as evidenced by the incline in PO4, which is not supplemented, recent liberal feedings of both fresh frozen and sinking green account for a considerable fraction. For now, I am reducing the daily KNO3 dose from 70 seconds (11.6 ml) to 40 seconds (6.6 ml). I will certainly have to make further adjustments, but will avoid getting on the low side of 2 ppm again.
I am not so enamored of the Hanna photometric nitrate tester as before. It's been difficult keeping tabs on NO3 and I have become suspicious that the variability has more to do with anomalous behavior in the instrument than natural fluctuations in the actual concentration. It is not a question of calibration; it is simply not consistent. Results are not repeatable, not even closely. I have been getting a lot of "check sample" error messages despite very careful adherence to instructions; wasteful of time and reagents and not very confidence inspiring. After running the same sample multiple times and getting widely disparate results, and also comparing to the simple API test as a reality check, I cannot rely on the numbers the Hanna tester is reporting. It has left me arbitrarily choosing which numbers I believe; not what is wanted in any test.
The API test gives repeatable results and is consistent. It is not precise in the sense that the photometric method is, but its accuracy is adequate for the purpose. I can easily see gradations ranging according to the following descriptors, and this will be the reporting protocol henceforth.
<< 5 ppm (significantly less than 5, but greater than 0)
< 5 ppm (close to but discernibly less than 5)
> 5 ppm (close to but discernibly greater than 5)
>> 5 ppm (significantly greater than 5)
< 10 ppm (close to but discernibly less than 10)
The Hanna photometric Checkers used for KH, iron and phosphate are precise and accurate. I like these a lot and continue having faith in them.
It's early days yet, but, tentatively, the amount of NeoMag, the rate of flow through the reactor, the dose rate of MgSO4 supplement, and the streaming water change regime seem to be finding balance. The Ca : Mg ratio does not comport with my earlier bias as to ideal proportions, but both numbers are high enough for aquarium plants so I will not be obsessing over that. The GH remains in the decidedly "soft water" category.
Not done yet regarding nitrate testing. The possible problems with the way I have been using the photometric tester do lie in the sample prep. When I take a 250 ml (1 cup) sample from the aquarium, almost always just after the morning dosing, I strain it through a fish net to remove debris. First problem, photometric testers are going to be sensitive to suspended matter. The sample should be passed through filter paper; a net or ordinary strainer is not adequate. It would be best practice to filter the sample this way for any test. It is easy enough to contrive an apparatus for pouring the sample through a coffee filter. This was done for today's sample. There were no "check sample" errors today.
Second problem, I have recently noted (16 March entry) the sudden dip in redox that occurs every morning upon dosing. This time of day is when the chemical oxygen demand (COD) is high and redox is actually unstable. The presence of strongly reducing and oxidizing substances, and also of protein hydrolysates, will interfere with the Hanna nitrate test (explicitly stated in the directions), and is probably not an ideal condition in which to conduct any chemical test. The dosing occurs between 07:00 and 07:20, just after the last AM open drain event, six hours before the first PM ODE. As a rule, the sample is taken between 07:30 and 08:00. Tests are run between 08:00 and 10:00, as was the case today.
I ran the Hanna photometric test three times and the API reagent test three times. The results:
Hanna: 1st test 7.6 ppm, 2nd test 6.4 ppm, 3rd test 7.0 ppm.
API: 1st test 5 ppm, 2nd test << 5 ppm, 3rd test << 5 ppm.
What to make of this? Is each test result within a realistic margin of error? The photometric tests are implying that NO3 is 7 ppm, + or - 0.6. That is certainly plausible. The data are such that I can draw no other conclusion; I could get a higher level of confidence if I took an average of more tests. The reagent tests are more problematic. I asserted that the API test is consistent, but, on this occasion at least, that is not the case. If the photometric test is anything close to real, the API test is low by 2 ppm, at best. I could put this down to two different kinds of tests with differing accuracy tolerances having an expected, but not trivial, differential. But the two follow on API tests, showing significantly lower values still, puts this interpretation in doubt. There is just something really wrong here. I will admit for the record that I believe that the NO3 concentration in this aquarium at the stated time of day is closer to 7 ppm than << 5 ppm.
For several reasons, I fully expect that NO3 will be different at 15:00 or 16:00 this PM.