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10.5 SUGGESTED REDOX POTENTIAL LEVELS:
Rarely will you see a complete listing of suggested redox potential levels, and rarely will they be qualified. Below is such a table, painstakingly arrived at after many years of testing and observation of many a tank (mostly tanks in my own basement and home). It involved keeping notes and charts in a total of 7 different notebooks.
These numbers can be used as really safe guidelines. I fully stand behind them, having arrived at them through a lot of empiric evidence and observations by myself and others who were asked questions about tank appearance in general, specific animal appearance, macro-algae growth or lack thereof, micro-algae growth or lack thereof, fish appearance, and so on.
These millivolt ranges apply in aquariums with a medium to high load (not a heavy lead), with a pH of between 8.15 and 8.25, a temperature of around 76-77 deg Fahrenheit, and a salinity of 35ppt (0/00). Because of the type of filtration used on the tanks tested, the dissolved oxygen levels were always at saturation or higher. Columnar and venturi protein skimmers and ozone were used as well.
Look at the numbers carefully and determine where your tank fits in. If you are not in the right range, use one or several of the many methods suggested in this book to increase the redox of your tank.
Very little will be alive : below 100 millivolt Very Bad : below 140 millivolt. Bad : 140 to 180 millivolt Poor : 180 to 200 millivolt Too Low : 200 to 220 millivolt New salt water : 220 to 240 millivolt Low : 220 to 270 millivolt Medium : 270 to 310 millivolt Good : 310 to 340 millivolt Better : 340 to 360 millivolt Best : 360 to 390 millivolt High : 390 to 450 millivolt Too high : over 450 millivolt Dangerous : over 525 millivolt Very dangerous : over 575 millivolt
All readings were taken using a platinum, silver, silver chloride electrode, cleaned on a regular basis. Several controllers were used:
Sander, WTW, and TAT. Readings were taken after the lights had been on for two hours. Metal halide lighting of three different kinds was used during the course of the experiment over the aquariums: Osram Power Stars, Venture Lighting 4300 K, and recently the new Coralife 5500 Kelvin degree bulbs.
Because redox potential is such a sensitive and changing measurement, you must be careful when comparing these values to the ones in your own tank. Pay attention to the type of electrode used and the conditions existing in your own tank, especially the pH.
No one level is ideal, but from the chart above it is easy to see that the range of 360 mv to 390 mv is obviously a very desirable one to be in. Aquariums can be maintained for short periods of time at higher levels, but you must pay careful attention to all life forms in the tank if you do. If they react negatively you must lower the redox immediately by, for example, switching off your ozonizer, or adjusting the set point on your redox controller to a lower number.
Many German hobbyists tend to run their tanks at slightly higher levels than the ones suggested here: often around 430-450 mv. This is still in the safe range, but on the high side of it. They report that it greatly reduces the annoyance of micro-algae.
My personal experience with running aquariums at the recommended redox potential levels is of a different nature. Yes, micro-algae problems were far less a factor, in fact, it was a non-issue, but that was, in my opinion, mainly due to extremely low levels of nitrates and phosphates in my tanks. I keep nitrates below 5 ppm of NO3, and phosphates below 0.05 ppm of PO4.
What I was able to notice over and over and document as well, is that corals open wider, so-called picky fish eat without any problems, and the overall tank appearance, all greatly improve at the suggested levels of 360 to 390 millivolt. You may want to experiment and see it for yourself.
10.6 WORKING WITH REDOX POTENTIAL LEVELS:
Knowing your redox potential value is one thing, being able to interpret and use it is yet another matter altogether. Once you have the value in the right range, its absolute number becomes less important, it is mostly the trend that you are and should be interested in.
To illustrate this premise we will use an example and some redox potential values, and then take a closer look at that aquarium's conditions and water chemistry:
(Conditions: Tank 100 gals, pH 8.2, salinity 35 ppt, Temp 76 deg, load medium, D.O. saturation, Lights on at 9.00 am and off at 9.00 pm.)
10.6.1 AQUARIUM WITH STABLE READINGS OVER 5 DAYS:
Redox 7.00 10.00 15.00 19.00 22.00 Day 1 401 387 379 375 391 Day 2 400 389 375 375 394 Day 3 398 384 374 370 396 Day 4 397 386 377 371 392 Day 5 397 388 372 373 390
As you notice, the readings are taken 5 times a day, and all exhibit a fairly stable value over a period of 5 days. The values are all in the correct range (360-390 for the majority) and the tank shows no signs of stress.
Take, for instance, all 3.00 pm readings (15.00 hours): 379, 375, 374, 377, 373. All are within a narrow range and no great fluctuations exist. The same applies to values taken at other times of the day, either before the lights are on, or even when the lights have been off for a while.
Because the trend is good and does not fluctuate up or down much, these can be considered readings taken on a tank that must be doing very well. And so it was. It looked in real good shape, animals were wide open after the lights were on for about 1 to 2 hours, and no micro-algae could be seen except for some very minimal amounts if one looked carefully. So little that it was actually beneficial to the overall look of the aquarium. What I mean by the latter is that the tank did not look like a sterile environment.
10.6.2 AQUARIUM SHOWING SIGNS OF STRESS:
Redox 7.00 10.00 15.00 19.00 22.00 Day 1 390 355 346 340 358 Day 2 386 354 347 344 356 Day 3 384 354 342 340 355 Day 4 384 355 340 339 354 Day 5 382 350 338 338 350 Day 6 381 351 338 336 353
In this example, although all redox numbers are still pretty close to the suggested best values, one can notice that over the course of 5 days all values have somewhat dropped. Look at all values taken at 7.00 am, or all values taken at 7.00 pm (19.00 hours), and see for yourself that they are slowly, but surely, going down.
This is an indication that the water quality is slowly deteriorating. Ever so slightly, but the discerning hobbyist will take that as a message that he or she better find out exactly what is happening "before" the situation really gets out of hand, and problems that are much harder to deal with start. Keeping records of what is happening becomes, therefore, even more important. Without records you will not know what the trend is.
We are not suggesting that you take five or more readings each day. Such is not practical for the majority of hobbyists anyway, but you can certainly record two or three. Usually one or two can be taken early in the morning, with one being a minimum. Two should be taken in the evening, one some time before the lights go out, and one after they have been out for about an hour to two hours. Such readings will give you enough material to work with and will tell you what the redox value's tendency is.
Looking at the trend obviously tells you whether you are in the recommended value range, but it tells you much more because you can see by the numbers whether your aquarium water is stable, or going up or down in quality, depending on how the redox potential values move.
When an action/reaction on your part is necessary, it can be planned and taken care of sooner and before things really get out of shape completely. This can save your animals and the looks of your tank. For example, a dropping redox potential may be an early indication that a fish has died, and that you need to find it and remove it from your system before too much pollution is added to the water.
10.6.3 AQUARIUM WITH FALLING REDOX TENDENCY:
In such aquariums the redox falls continuously over a period of a few hours, and nothing seems to be able to make it rise again unless, of course, some type of action is initiated by the hobbyist. Which particular one is not relevant at this point. It will be any of the ones mentioned already, but more likely than not, a combination of several.
A falling redox potential may happen slowly, as in the following example of two days' readings:
Day 1 396 379 372 taken at 7.00 and 10.00 am, and 10.00 pm Day 2 355 343 331 taken at the same hours one day later
In each case the readings have fallen substantially from the previous day, a definite indication that something is wrong, and that some sort of action is required to counteract this effect.
Or it may happen much faster. For example, if the readings taken on the first day, at the same times, showed redox potential values of respectively 326, 299, and 264 mv. Obviously, in this particular case trouble is already at hand, because the numbers are falling so rapidly.
10.7 INFLUENCING THE REDOX UPWARDS:
It should be fairly clear by now to you that increasing the redox is not just the result of one action. Redox potential values rise when a combination of factors favorably influence it. Most of the ones commonly used have been described either in this chapter, or in other parts of the book.
Follow the suggestions made and your tank will definitely improve in water quality and appearance in a matter of a few weeks or less. Plan on using a really efficient protein skimmer, with ozone, and low redox values will be a matter of the past.
Keep your maintenance and husbandry up and your redox will stay high. Do not overfeed and do not overcrowd the tank and you will not have to upgrade your filter, as long as it was correctly sized the first time around. Even when using an efficient skimmer, make sure that you change the air stones frequently. Loss of efficiency because of worn out air stones is very common, and can so easily be avoided.
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