What is a stable system??

[mdmaquatic]

Question everyone....What is considered by most of you as a stable system??? How much salinity/temp/PH fluctuation can you allow before you get out of that "stable" system criteria?? I know that especially on holding systems like we have it can be hard to compensate for the fluctuations. I was just curious what people thought. Also second question,what does everyone keep their salinity at?? Some say 1.023 some say 1.025... what does everyone out there keep them at??

[Reefland]

Mike,

Stable means a couple of different things to me. First of all it means that the system is established enough biological filtration that covers the addition of new coral or fish, without any worry that the additional bioload is going to affect the critical parameters; ammonia, nitrite or a large increase in nitrate. This also means that your other critical's such as pH, temp and salinity are steady. Secondly, I like to think that a 2 degree temperature swing and a .5ppt or 1.001 swing in specific gravity are maintained.

As far as what to keep the salinity at, I think 1.025 or 1.026 is better for coral systems. 1.023 can be used for FO systems but is less natural.

[Ninong]

How much salinity/temp/PH fluctuation can you allow before you get out of that "stable" system criteria??

The answer to your question depends on whether you are asking for ideal, but unattainable, conditions or merely tolerable conditions.

Daily salinity fluctuation should not be a problem for most hobbyists, yet it often varies significantly in the wild in shallow lagoons during rainstorms. Even entire regions (e.g., Gulf of Thailand) undergo large seasonal variation in salinity between the dry season and the monsoon. The salinity of areas that are under the influence of nearby deserts, such as the Red Sea, will be much higher than the open Indo-Pacific. The salinity of the Red Sea varies from 39 ppt to 42 ppt -- higher in the northern part than in the southern part. The salinity in the Mediterranean averages around 37 ppt most of the year. The salinity in surface waters near most tropical reefs ranges from 34-36 ppt, with 35 ppt being average. Daily and seasonal fluctuations vary from region to region depending on rainfall patterns and the depth of the water. Even in areas of deep water, the upper layer of lowered salinity caused by heavy rainfall will float on the full strength seawater beneath.

Salinity stability is probably the easiest water parameter for the average hobbyist to maintain.

Temperature fluctuation on a daily basis should be minimized. That's easier said than done unless you are running a chiller. If you are not running a chiller, a diurnal variation within a range of 3 to 4 degrees Fahrenheit is tolerable. Anything more than that is risky. I have had significant problems with daily temperature fluctuations that exceeded four degrees. I finally purchased a chiller and hope to control my temperature +/- 0.5 F by using my Neptune Systems Aquacontroller instead of the chiller's controller.

A daily pH range of two points would be ideal, a range of four points is more likely for most systems. My pH usually ranges from 8.1 to 8.3 but it sometimes drops to 8.0 and occasionally reads 8.4. I would hate to see it drop below 7.9 or rise above 8.5.

Also second question,what does everyone keep their salinity at?? Some say 1.023 some say 1.025... what does everyone out there keep them at??

Before I answer your question, I have to point out that specific gravity without the corresponding temperature is not a precise statement of your salinity. The density of water drops as the temperature rises, so a reading of 1.025 SG at 84 F is a much higher salinity than 1.025 SG at 76 F. Now that refractometers are commonly available, perhaps we should stop quoting meaningless specific gravity numbers?

I try to maintain my reef tank at 34-35 ppt salinity. If I were setting up a system devoted to Red Sea species exclusively, I might keep it at 37 ppt. If I had a fish-only system I would probably keep it around 34 ppt. Some people keep fish-only tanks at 30-32 ppt in the mistaken belief that lower salinity is easier on the fish, making it easier for them to osmoregulate, but studies have shown that it makes no difference. It takes about the same amount of energy for them to regulate in full strength seawater as it does in lowered salinity seawater. So the advantage of lowered salinity in a fish-only system would be found in cost savings on salt mix and lowered susceptibility to parasitic infestation.

I don't know if one can say that lowered salinity has any negative effects on long-term survival (of fish) or not. You can't compare survival rates in captivity against natural lifespans because large, stable captive systems are less stressful than natural conditions and fish tend to live longer in stable, well-maintained, very large public aquaria than they do in the wild.