never saw anyone else do such so thought i'd share as it looks very neat. if this is old idea then just ignore.

i got this idea from watching some under ocean footage on tv of the kelp reef years ago. maybe others here have done this before but anyway, the beams of light and caustics, shadows on the surface moving with the waves above was very relaxing. so i mimic the idea in my aquarium using only aluminum foil.

so to cause shadowing and light rays (caustics) in the tank.
simply take some aluminum foil and cut it to the size of the plexiglass on the hood *top of plexi and under your light.* just lay it smoothly so it covers the plexi. cut a very few holes in it, experiment for taste but 1/4 inch holes every few inches apart works pretty well, start with one or two holes depending on length of tank and add or resize to liking. if your lights are bright like mine, more holes make less shadows and no rays. smaller holes spread out well causes some nice light beams but does dim your tank but i bet your fish wont mind, no one likes bright flourescents in their eyes

....anyway, when you lay the foil on top of the plexi, then the light over it as normal, the light is focused through the holes causing rays of light to beam into the water which also causes the ripples in the water to create shadows on the surfaces in the tank.

The aluminum foil never gets hot, well not enough to damage plexi, i use flourescent light but if your bulbs put out alot of heat, use your own judgement and check it after a few to make sure the heat isnt excessive under your light. I've done this for years and never any problems but again check how hot your bulbs are cause this will hold in a little more heat than normal in the space between light and aluminum foil.

The effect is very relaxing and adds some natural realism to it. if you cant picture it, then maybe you've seen the screensaver called "Sim Aquarium", all the ripples on the surface of the water are reflected onto the surfaces below.

this pic here is similar to what you can expect. Color light such as blue or green would look really nice as well. green light should look more like this pic but you get the idea

I am not a salty person but don't you need the light for corals and such to thrive? By laying the foil on top, you are cutting the light dramatically. I do like the look but worry about what else you may be affecting.

__________________
Fishless cycling

i use freshwater and failed to mention the idea is intended for such, but obviously if you have tanks requiring lighting for survival then this isnt such a good idea. i dont know if there is an alternative method to do this and maintain adequate life for growth, but where theres a will, theres a way.

i should have mentioned that, naturally everyone should use their own judgement. my tanks have always been fake and probably a good idea to do this only for artificial setup's.

thats awesome

Well night time is night time, if you have have a double lid where during the day all the light gets threw and at night change to the night time one , i dont think it would do any harm. at all. would just take yah time up changing perspex top.Good idea though.

I have to agree, that is an absolutely wonderful effect and I have some tanks that the fish are not wild about bright light in and would love this I am sure. But in a planted or salt tank it would be a problem perhaps.

But I do love the effect and want to thank you for sharing this.

It is marvelous and so simple.

Rose

This would be a nice thing to try with actinic bulbs on a freshwater setup. I may just have to experiment with this on the larger tank. All other tanks the lights hang above them so not sure it would work will in high light planted tanks.

But....actinics at night....could be pretty kewl in a freshwater setup.

this is a very cool trick, i wish i had somewhere i could try it

you can do this another way also, all you need is surface movement and high intensity lighting like metal halides, all of my friends that MH's get this affect

__________________
It has become more than a hobby! My 29gal Dream Reef DIY Build

i do this by simply putting a light further above the surface and the bubbles and filter disturb the surface causing this affect on the gravel.