Why is my tank water constantly turning green?

[DJasak]

I have a small 16 gallon tank that seems to like to turn completely green on me in only a couple days. Its just a simple little set up I have in my son's room i use as his night light. I orginally had glo fish in there but that seemed to turn greener faster than if I just stuck to saltwater. Ive had to completely drain, clean, and refill the tank a couple times this year because it got so bad I didnt have much of a choice. During the day the lights stay off. And if nobody is in that bedroom I make sure the room lights are off. My son is only 10 months old so we don't spend much time in his room, so lights are almost always off other than when he goes to bed. I also have black out curtains on his window so no outside light is shining into his room. And for the past month I've had no fish in his tank. I was cycling the tank when I had the ammonia spike happen while I was away and I was only able to save 1 of the 3 fish. Since then I've left the tank empty with just sand and rock in there with the filter running. I do a water change every 2 weeks, but this month I only did it once (about a 35% water change) I can't figure out what makes this tank turn so fast. I just did my 2nd WC for the month and I put a blanket over the tank in hopes that it'll kill off all the algae. Any suggestions would be great! I'm not doing anything fancy on this tank just ur basic hob filter, heater, and fluorescent bulb. Lights are turned on for about 12 hours and that's while he sleeps. During the day the tank and bedroom stays dark. I only want to put 2 or 3 hardy fish in there to entertain him and that's it. Please help!

[chimmike]

what's the water temp?

[scooter31707]

My first impression would be some type of algae bloom. Are you using RO/DI? How many fish are in there and how much are you feeding. Do you have good circulation in the tank. How old is the bulbs in the light fixture? These are some things that can cause an algae bloom, if this is the case.

[chimmike]

sounds like no fish in the tank currently.

water source is a good question.

[A1t2o]

Maybe you should grow some sea grass in the tank. 12 hours is a long time to have lights on so it could just be that there is enough light for algae to grow. If you throw some macro in there and have that soak up the nutrients while also providing a place for fish to hide and also supporting pods. Could be really cool to have a sea grass/macro algae tank. Plus if you have tangs in your main tank, then you could feed them with cuttings.

[Sk8r]

Phosphate load, likely. It's algae. There are filters that can remove it fast (diatom filter) but a bit of overkill for a tiny tank---filter's nearly as big as the tank. If you have a spare GFO unit, running that, changing media monthly, could solve it. And of course use only ro/di water.

[gone fishin]

Depending on what type of fluorescent bulb you have it may be in the great for algae spectrum. I would also consider upping the WC schedule to weekly. Good luck just my 2 cents.

[DJasak]

Thanks guys! In the tiny tank I've just been using tap water. In my main tank I use distilled water. Temp is at 78. I like the macro idea! Only bad thing is I don't know where I can find decorative macro for sale. No fish in the tank currently. I've been using only distilled water for over a year now. I just never bit the bullet to buy an RO/DI unit (even tho I could have bought 2 of the 4 chamber set ups by now. Lol) after the holidays I think I'll pick one up. Thanks again!

[DJasak]

Oh and the light bulb is about a year old. It came with the tank ensemble when I bought it

[chimmike]

well uh. that's your problem then, the tap water.

You should know this?

[Dundermifflin]

RODI....big difference v. tap!

[DJasak]

Well I know Rodi is better than tap but I didn't think it would make my water turn green. I had freshwater tanks for years and all those I used tap and never had an issue