Lighting In An Unplanted Aquarium... Should I Structure It?

[simonero]

Hello!
 
I recently bought a light for a tank that doesn't have and will never have plants, and realized that I have no idea if I should be determining my lighting patterns based on something.
 
I have 3 very large apple snails in the tank so all plant matter is food by default and gone within a few days.  There are a bunch of guppies and 2 goldfish...  Trumpets lurk around too.  That's it.  (It's really just a snail tank that I also use to separate my guppies so I don't over-populate...)
 
No visible algae at all with consistently no added light or the light on all the time.  Also, with the number of snails in there, I'm not worried.  I don't care about algae regardless, as long as it isn't detrimental to tank health in any way.
 
I've turned the light off or down to the "blue" setting a few times recently just because the weather has been a little warmer, but I don't want to turn off the heater and have a temperature spike overnight.
 
Other than that, is there any reason to have a routine or set cycle for when I turn on the light, or what setting my light is on? (regular bright LED vs low light blue vs OFF).  Will changing the light based on my sporadic preferences put any unnecessary stress on my tank?
 
Thanks in advance, I appreciate your input!  

 

[Blondielovesfish]

Just curious, what temperature is your tank at?
The only reason why I ask is because Goldfish are coldwater fish, but guppies are more tropical.
Also, what size is the tank?
 
Having a regular daylight cycle is good for the fish, as it gives them a good routine in terms of day/night etc.
The general rule for how long a light is on for is 6-8 hours, however since you're not worried about algae, you could go to about 12 hours, although if the weather is hotter, then you'd be better off having the light turned off around midday, or coming on after the hottest part of the day.
 
Some people do say that the fish don't really care about the light routine, but I personally believe that it is better to give them a proper day/night cycle as it reproduces to some extent what they would encounter in their natural habitat.

 

[simonero]

It ranges between 73-78F, not by day but in general (not a new tank).  I avoid temperature spikes but weather does lead to changes.  I lived in FL and recently now GA so I'm not talking anything drastic, but enough to need a heater basically.
 
I have read that about goldfish - this sounds bad, but other than proper feeding I'm avoiding tailoring the tank to them.  In August I cycled a new 55gal with 13 of them (only because of limited options and time when moving - I had one day to set up and all I could find was a Petco) and these two made it.  They were feeder goldfish so I figure keeping them for as long as they live is better than giving them back..... to still be sacrificial goldfish.....
 
The tank is a 20 long.  Not too big.  The light was marketed for a 20gal but I don't know enough about lighting to determine how much I can trust that arena of marketing.  Light is a very new thing for me.

 

[Byron]

On the light and fish issue, Leonie is correct that fish are affected.  I researched this for an article a couple of years back, so here is the relevant data copied from the article.
 

[SIZE=12pt]Lighting: How It Affects Freshwater Fish[/SIZE]​

 
Fish are affected by light in many ways.  There are several well-documented studies on spawning in some species being triggered by changes in the day/night cycle, and the hatching of eggs and the growth rate of fry can be impacted significantly depending upon the presence and intensity of light.  The health of fish is closely connected to the intensity of the overhead light, various types of light, and sudden changes from dark to light or light to dark.  To understand this, we must know something about the fish’s physiology.  The primary receptor of light is the eye, but other body cells are also sensitive to light.
 
Fish eyes are not much different from those of other vertebrates including humans.  Our eyes share a cornea, an iris, a lens, a pupil, and a retina.  The latter contains rods which allow us to see in dim light and cones which perceive colours; while mammals (like us) have two types of cones, fish have three—one for each of the colours red, green and blue.  These connect to nerve cells which transmit images to the brain, and the optic lobe is the largest part of the fish’s brain. 
 
These cells are very delicate; humans have pupils that expand or contract to alter the amount of light entering the eye and eyelids, both of which help to prevent damage occurring due to bright light.  Fish (with very few exceptions such as some shark species) do not have eyelids, and in most species their pupils are fixed and cannot alter.  In bright light, the rods retract into the retina and the cones approach the surface; in dim light the opposite occurs.  But unlike our pupils that change very quickly, this process in fish takes time.  Scientific studies on salmon have shown that it takes half an hour for the eye to adjust to bright light, and an hour to adjust to dim light.  This is why the aquarist should wait at least 30 minutes after the tank lights come on before feeding or performing a water change or other tank maintenance;  this allows the fish to adjust to the light difference.
 
The Day/Night Cycle
 
Most animals have an internal body clock, called a circadian rhythm, which is modified by the light/dark cycle every 24 hours.  This is the explanation for jet-lag in humans when time zones are crossed—our circadian rhythm is unbalanced and has to reset itself, which it does according to periods of light and dark.  Our eyes play a primary role in this, but many of our body cells have some reaction to light levels.  In fish this light sensitivity in their cells is very high. 
 
Previously I mentioned that the rods and cones in the eye shift according to the changes in light.  This process is also anticipated according to the time of day; the fish “expects” dawn and dusk, and the eyes will automatically begin to adjust accordingly.  This is due to the circadian rhythm.
 
This is one reason why during each 24 hours a regular period of light/dark—ensuring there are several hours of complete darkness—is essential for the fish.  In the tropics, day and night is equal for all 365 days a year, with approximately ten to twelve hours each of daylight and complete darkness, separated by fairly brief periods of dawn or dusk.  The period of daylight produced by direct tank lighting can be shorter; and the period of total darkness can be somewhat shorter or longer—but there must be several hours of complete darkness in the aquarium.  The dusk and dawn periods will appear to be stretched out, but that causes no problems for the fish.  It is the bright overhead light that is the concern, along with having a suitable period of total darkness.
 
There is much more in the article, but I think the above excepts answer the present question on the light.  There should be a consistent period of "light" and a consistent period of darkness during each 24 hours.
 
I would not leave the two goldfish in so small a tank, even though I understand your reasoning, because it is simply no where near sufficient space, and they should not have heated water permanently.  Does anyone have a pond that would be a better home?
 
Byron.

 

[simonero]

Thank you so much!  Both of you!  That is immensely helpful.  I'm going to get a timer.
 
Unfortunately, I am in a new town and know nobody who wants to or is competent to take care of a fish better than I can (which I do not mean to say presumptuously - I just really don't know anybody who cares about fish!  Or many people yet in general.)  My extensive attempts to re-home another fish were wildly unsuccessful as well.  Atlanta is a bad place to love freshwater fish.  My only other option, if I wanted to adjust the temperature, would be to put them in a ~2gal tank with a filter that takes up a lot of the space.  They seem better off in the larger tank.. they end up with a diverse diet of plants, carrots, spinach, spirulina, guppy fry (that's GOT to be the reason the population is under control..), and I think they may be eating snail waste for me too 

 
I'm thinking that perhaps once they have grown larger it'll be worth a shot looking for a new home (that won't just feed them to something).  Unless they reach a size that my angel fish won't keep trying to murder them.  They lasted less than a day before I had to put them back in the smaller, more-stocked tank.
 
As far as the lights - it sounds like I should get a timer, like I have for my big planted tank, but I do have one final question.  What is the deal with the regular LED light and the blue light?  Given I'm not growing anything, what effect does one vs the other have on my fish (for the "ON" period?)  It is just build that way as a novelty to get people to buy it or is it useful in some way?
 
Sim

 

[Byron]

A lot of aquarium lighting is geared toward marine tanks, and blue is the predominant wavelength because corals need this, and marine fish tend to look natural with a mix of blue and white, or "cool" white light.  Freshwater fish tend to look best under warmer light, which means less blue and more red in the mix.
 
The colour temperature of light is expressed in Kelvin.  Light with between 5000K and 7000K will render colours naturally for the most part.
 
Byron.