Diatoms won't stop please help?!?!?

[james_r_edwards34]

I am getting brown algae "dusting" on everything and it is going crazy. It won't stop. It started about a month ago. The tank has been up for over 6 months and was starting to get coraline algae all over the place, in which the diatoms are killing off. I believe it is diatoms from what I have read. I have a 125 gallon aquarium, fluval FX5, and a koralia powerhead. There is an average of 3" of live sand (4" at deepest point) and maybe 80 lbs. of rock. I have not hooked up a skimmer yet. I have the Coralife 72 inch power compacts with (2)50/50 and (2)daylight spectrum bulbs. I have done water changes, and changed out the activated carbon. I am using Kent Marine Essential Elements (trace elements) and Purple Up. There is a very thin oily film on top of the water. not visible from top of the water but if you look up through the aquarium it is visible where the water current isn't as strong. Please help I am so frustrated.

[ricksreef]

Diatoms need silica to grow, so I'd suspect your source water for that.
instead of carbon, I'd run chemi-pure elite. it has phosphate and silica medias added to it.
I'd also drop the trace elements to 25% of recommended dosage.
and either use up or get rid of the purple up and switch to good calcium and alkalinty supplements (I love oceans blend two part).
The oily film is built up proteins and a skimmer would deal with a lot of it. but without and overflow box/surface skimmer, it can be tough to totally eliminate it. drapping and dragging paper towels across it can help pick it up.
as a side note, it's also possible that the film is reducing spectrum and par to favor the diatom growth.

[reefplayground]

Well, there could be several things fueling the growth. There are also some info needed about your system as well.

What kind of water are you using for water changes? and what is its TDS?

Your statement about an oily residue on top of the water suggests there is an excess of nutrients in your system, phosphates, nitrates, and/or other organic compounds. The addition of a protein skimmer will help remove this organic waste.
You can also use Seachems Purigen to remove the organic waste.

I would also suggest to cut back on the dosing Kent Marine Essential Elements as this is simply feeding the algae bloom.

[james_r_edwards34]

Thanks for the info I will try all suggestions. I am using the "bulk" bottled water from Kroger (grocery store chain in Midwest). The water is supposedly filtered through RO, then carbon, then a uv sterilizer. I will reduce the dosing of trace elements and change the food I am using. I will go for the chemi-pure as well.
Thanks for reading and responding.

James

[reefplayground]

The water may be the source. Those water filters are generally not that efficient. I've tested the TDS on one we have in my area, came out at around 40ppm. (should be at zero).

[Ninong]

I suspect that the problem with the various water vending machines (such as Culligan's in Wal-Mart, et al) is that their scheduled maintenance (such as changing the membrane, etc.) is based on the calendar and not actual usage. This might explain why hobbyists using the same store's vending machine sometimes report different TDS measurements. Of course if you're buying the more expensive 'pre-bottled' by the manufacturer purified drinking water, then there's no excuse for high TDS.