View Full Version : Should I test these parameters with a spectrophotmeter or with test kits

08/17/2018, 03:33 PM
I posted this thread elsewhere, but did not receive any replies. Maybe someone here can help. I'm putting together a tank for the first time, 90 gal.

I plan to test for the following:

Temp, pH, and salinity are straight forward. I have no questions regarding these.

For Ammonia and Nitrite, I only plan to test these to determine when cycling is complete, or if I’m having a major problem with the tank. I plan to get the cheapest tests possible, since accuracy isn’t important. When cycling, when ammonia and nitrate read “zero”, I’ll wait a week or two to make sure levels are truly at zero, then stock the tank. Do you see any problems with this approach?

As for the rest of the tests, things get tricky. There are three issues that I have to consider: how accurate I need my results to be, costs, and how much of a pain the test is to carry out. I have a vintage 1970s spectrophotometer that's worth about $40, but it still works. I can use if it makes sense.

If I use the spectrophotometer at all, there will be some fixed costs. For each additional parameter I test with the spectrophotometer, I’ll have some significant start up costs since I need to use reagent to test pure ionic compounds to get reference plots in order to interpolate my experimental results. For me, all this represents significant expense. Thereafter, once everything is up and running, the running costs of the spectrophotometer will be about 50% higher than they will be for reagent kits.

So, I can use the spectrophotometer, reagent kits, a combination of the above, or if I’m only going to run one test with “light readings”, I can buy a Hanna colorimeter.

I don’t know what to think about testing phosphate. On the one hand, I feel that if I use a cheap test kit and have bogus readings of zero, or some number which is lower than 0.1 ppm, and my chaeto stays alive, I should be fine. On the other hand, it might be important to have a fairly accurate reading of phosphate for the health of the chaeto, and to make absolutely sure my concentration is below 0.1 ppm. My gut reaction is that an accurate reading isn't important, but I don't know.

As for nitrate, I'd guess a cheap test would be fine. As long as it's somewhat accurate, and can tell me when I'm below 5 ppm I'll be fine. Does this need to be tested accurately?

As for Alk, Ca, and Mg, I don’t know how important accuracy is.

In all of this, there are people that run tanks for decades using only test kits. I'd like to keep pH above 8 at all times if possible, and up to 8.2-8.3. So, some of these parameters might require more accuracy than they would for others. Maybe "accuracy" of readings is all relative.

So, regarding NO3, PO4, Alk, Ca, and Mg, considering the importance of accuracy and the hassle of doing the tests, do you think I should go with the spectrophotometer or the test kits?

Thanks, I really appreciate it.

08/17/2018, 03:57 PM
For now, test just test your NH3 -> NO2 -> NO3

Worry about everything else later.

Test with regular saltwater API kits for the parameters stated above.

When you advanced to the next stage, use more specific test kits for your parameters

Sent from my SM-G955U using Tapatalk

08/17/2018, 04:32 PM
So, regarding NO3, PO4, Alk, Ca, and Mg, considering the importance of accuracy and the hassle of doing the tests, do you think I should go with the spectrophotometer or the test kits?

I would guess that the average aquarist can be successful using test kits because most the test kit chemistries are good and color chart comparisons are fairly straightforward. Kits might differ in ease of use or ease of color intensity determination.

The spectrometer is nice in that you can obtain a more objective and quantitative observation of test color intensity. The Hanna Checker is a bridging technology between the spetrophotometer and “eyeballing” color intensity.

The simplest approach is to decide later. Start out with test kits and determine whether eyeballing color intensity provides the accuracy and precision you want. If not, start taking absorbance readings of the test kit solutions.

08/18/2018, 06:39 PM
I think that waiting for a week after reading zero ammonia should be fine for getting going. Nitrate isn't very toxic, and neither is nitrite, in the levels we see it, so you could skip those kits for now. The same goes for phosphate.

pH is marginal in utility. Most tanks do well enough for pH, and it's difficult to do much in most cases where it's a bit low. Generally, fresher air is difficult to provide.

Alkalinity and calcium are important to measure if you want to grow corals or coralline algae. Otherwise, they can be ignored. Magnesium problems are very rare, so you could wait for signs of trouble before getting a kit.