plecos are known as armored catfish because they have a fairly tough outer skin. Many keep them in ponds with Koi
or with chiclids, which are more aggressive than Goldfish
. Getting that bluish hue from a bulb designed for reef aquairums may cause an algae bloom. Amount of light will be dependent on the bulb you use and plants. Since you ahve no live plants, a 12 hr light cycle may give you lots fo algae growth. Goldfish
and plecos are both some of the dirtiest fish available for hobbyists, so your nitrates will be fairly high, even with weekly water changes. a 12 hr cycle will give you too much food for algae. However, this is still dependent on your bulb. Find out what wattage bulbs you have now and what kind you would like. If your going for very bright powerful lights, then you may need to cut lighitng as far back as 8 hrs a day. Plecos are excellent cleaners but they make as much poop as they eat algae, so it turns into a messy cycle.
Leaving a light on for too long is something for every type of tank, not jsut Goldfish
tanks. However, as i stated before, a Goldfish
tank will need more maintence an light balancing to keep algae blooms in check. It is recommended that most aquarists do a water change each week, lower bioload tanks can get a change biweekly. A Goldfish
/pleco tank, using the inch per gallon rule, is a high bioload setup, which means either you change a large amount of water 20-30% weekly or do a 10-15% change every 4 days. <-- recommended. Of course your bioload also depends on how many fish you got, if you have less fish and a low bioload, less water changes will be ok.
Even at 50 gallons, golfish and plecos will take up a lot of space. Max size of a pleco is over 1 feet and Goldfish
often can get up to various large sizes depending on type. Using the very basic 1 inch per gallon rule, one pleco could take 15% f your tank space. Using bioload calculating, plecos generate a ton of waste so in actuality over 25% of your tank capacity is taken. a pair of Goldfish
at around 4-5 inches, their bioload is really 16-20% so with 3 fishes, you capacity is almost at 50%, roughly 20 -25 gallons of water needed. You may know this already, but many do not and end up wondering why their tank is always yellow, cloudy, or covered in algae. If you do proper research and follow a similar bioload estimate as above, it will be easier to set up the tank so that you can have your lights on for 10+ hrs a day and less water changes.
As for supplemntal lighting, some aquarists do use LEDs for moon-light. How expensive it is is dependent on how much coverage you desire. I have a hydor moon light in my tank and i ahve it set to turn on as my main lights turn off. I have seen tanks with the LED lighting on 24 hrs a day and with the main flourescent bulbs on, you cant tell the LEDs are even there. Also note that the color the LEDs are in could affect your algae growth. Blue and white usually give more to algae if on for extended periods of time, especially in submerged LED setups.