I don't often need to seek help, however, I am going to ask for advice because I have a problem that is driving me around the bend.

About two months ago, my 125 gallon tank started going cloudy overnight. So of course the first thing I did was to check for ammonia and nitrite, both of which were zero ppm. Water changes are carried out on a weekly basis and the nitrate level is normally around 30 at the end of the week. The tank contains two Oscars, four clows Loach and 1 Jade eyed Cichlid. Anyway, it slowly got worse and worse until you couldn't even see the back of the tank. Water changes still carried out once a week, water tests once a week, absolutely spot-on. Decided to clean filters as they haven't been done for around four months, little bit dirty, but not really too bad and nothing to worry about. Still extremely cloudy and looking green. 50% water change made quite a difference in the cloudiness but it came back again. Last week, I bought some "Green away" the bottle was only enough for 500 L, around 50 m short of my actual tank. The next morning, not entirely clear, but a 90% improvement. A few days on, it started to get cloudy again.

So you can see my dilemma, tank lights are only put on in the evening for around three or four hours, I have backing on the side of the tank to stop sunlight entering the tank. Fish are fed once-a-day and they eat all the food.

Now I am wondering because I didn't put quite enough Greenaway in, this is why it's coming back. The problem is, Greenaway doesn't kill algae, it causes it to stick together so that the filters remove it, or it sinks. I'm going to treat the tank again next week, but this time with the right amount and see what happens. My mate who builds ponds, reckons if I'd put a small UV filter in line on the filter, it might help. I suppose it's worth a try.

So any suggestions from anyone would be very grateful, anything is worth a try

when i had this problem all i did was to follow yours and delboys advice and reduce the hours of lighting,cut back on the amount i fed them, and did larger than normal water changes, added some water clarifier and my issue went away in a few days. now im sure that you've done this so the only thing i can see is that perhaps it did come down to the amount of greenaway in your tank. however if yu do go with a uv filter you can hide it away in your sump.

if i find anything that might relate to your prob i'll be sure to mention it to you.

good luck with your water

if I reduce the time I have my lights at the moment, I won't be putting them on at all. There is absolutely nothing I'm doing to encourage the algae I think it's just a case of not treating the tank with the correct amount, I just didn't have enough. I'll try again next week and see what happens. The problem with algae as it can sap the oxygen from the water, so you have got to be a bit careful

Hmmmmm, Ive never had this problem but you seem to be doing eveything possible, I would do a water change and then add the green away. wait for greenaway to work then clean filter. This way, the greenaway will have the least amount to work on as the water change would have removed some too. Maybe do a extra change after ?? I think your PH has something to do with how greenaway works ?? If you have low or high PH you may need to adjust your PH for max effect. This could have something to do with why you have the problem but thats just a guess?? You dont have live plants do you?? as the plant food makes green grow quicker. This could also be your problem. If you dont have live plants( build-up of Nutrients making it nice for green) you could try carbon if it is this as the carbon will remove the phosphates. About a half kilo should do. I say this as I once tried live plants but found if I fed the plants the water went green too fast.

As you said the most common cause of green water is too much light. Light comes from 2 possible sources, tank lights and sunlight (the standard lights in your home are too weak to count)

The thing about sunlight is most people think about sunlight going directly onto the tank, but you can get reflected light. So suppose you have a white painted wall outside the window near your tank , you can get reflected light onto the tank. This light doesnt 'show' like direct sunlight but it is still light on your tank.

Try part closing or even fully closing your curtains. The cause of the green may be something else but it may be no coincidence that sunlight is bright this time of year

all sorted now.

I have absolutely no idea why my tank suddenly develope this green water algae.

Without sounding like I'm up myself, I certainly didn't do anything that would encourage this algae, after all, I have written plenty of advice on this website are regarding this. I suppose we will never know.

Anyway, some really good advice for anyone in the same situation. If you need to get some treatment to remove algae and you happen to have a large aquarium, get the stuff that is sold for garden ponds, not aquariums. It's exactly the same stuff in the bottle, only it goes a lot further. the first stuff I bought last week cost just less than £5, it was enough to treat 500 L, the tank I was treating was 550 L. It didn't quite remove all of the algae so I came back again. So I went back to the fish store and bought something with exactly the same name but for ponds, £6.50and treats over 1000 gallons. I only needed 12 mL to treat 125 gallons, and now it is beautifully clear.

That's cool that you tank got cleared up! You can get waterborne algae spores from lots of sources. I've gotten it from my garden hose. I've had this issue in the past so I've got to warn you. It is next to impossible to remove all of the algae from your water. You will have relapses periodically now that it has started. The next time your water clouds without any other apparent changes in water chemistry, assume it is algae and nuke it.

To anyone reading this, be very careful if you're going to go OFL's route and just hit it with pond chemicals. They are far more concentrated and if not properly diluted can kill your fishes within 24 hours. I've lost koi that way.

The algae can eventually build up an immunity to algaecides. Every algea fix I've ever purchased contained...

Poly(oxyethylene(dimethyliminio)ethylene(dimethyliminio)
ethylene dichloride)...Yeah that's all one word and yes i had to copy it from a label.

Anyway, they are all basically the same stuff. Once you've got resistant algae, shell out the money and get yourself a UV Sterilizer. These clump up the individual alga so that they can be removed though filtration. A 8-9 watt sterilizer is sufficient for a tank your size OFL. This WILL cure your problem within a couple weeks depending on your total algae load. You will never have the problem again running one of these. Guaranteed. UV Sterilizers irradicate all waterborne pests as well. I keep one running on my 125 year round. Just remember to replace the bulb every 12 months.

That's a good point, don't just dump it in willy-nilly. I use a plastic container which I fill with existing tank water, I then pour it over the whole surface of the tank. The fish will react slightly to this treatment, but it doesn't last too long. I think I am going to try the UV approach if it starts happening again, I don't really like chucking lots of chemicals into the tank, it can't do the fish any good in the long run.

This is also the case with white spot cure and i would say prob some other illness cures, Treatment for ponds are the same but you may need less than bottle says i.e, if bottle says 1 drop per litre and you have 5l you may need only to add 4 drops as pound stuff are for less sensitive fish and seems to be stronger. If you are unsure phone the company of the product, I found them always helpful.