Green Water - The Planted Tank Forum
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post #1 of 7 (permalink) Old 07-10-2004, 10:09 PM Thread Starter
Algae Grower
Join Date: Mar 2004
Location: Scotland, UK
Posts: 22
Green Water

Hi there.

I'm new here and I hope you can help.

I have a 650l (170 US gallon) discus tank which measures 5'x2'x2.5'. It has been running for 2 years now. Over the last few months it has went through an algae nightmare.

I stupidly decided to clean all the hair algae from the textured background (Juwel polystyrene stuff) and from then on in we have had nothing but trouble.

The tank has had blue green algae for months. Really thick, slimes of it. I did a bit of research and found that this is caused by high Po4 and low No3. As we have a discus tank we use RO water and the NO3 is usually 0. PO4 became highly elevated when I tried a pH 6.5 buffer with my RO (It was a PO4 based buffer). Through water changes and using Hagen Green X I have managed to get PO4 from >30ppm to ~5ppm. I have also started to add Poor Man's Dupla Drops in an attempt to supply a good mix of trace elements and add NO3.

Last week the BGA dissapeared over a period of 3 days. Fantastic I thought, we have finally beat it. Not so I'm afraid. The tank is now cluding up with what I can only assume is single celled algae.

PO4 = 5, NO3=10, pH 7.2, KH=0. Temp 29C. We have added a huge amount of plants in the vain hope that these will start to use up the nutrients. Once the BGA dissapeared they looked good and look like they are growing. We have 6x 42w tubes over the tank and do not add CO2 (the water is too unstable and the pH would crash).

Is this just a stage that my aquarium will go through to use up the final PO4? Should I stop adding the PMDD? Should I continue with water changes (they are now PO4 free).

Will this algae nightmare never end? I had a nice looking tank for 3 days in 4 months. Surely it can't go on forever????


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post #2 of 7 (permalink) Old 07-10-2004, 11:38 PM
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Hi Sharon, welcome to the Planted Tank, the best place to battle green water!

There are a few options here, and I will try to mention disadvantages of each one.

1) Do nothing. Sometimes GW will disappear by itself, because it is eating up that specific nutrient combination that it requires. For this to work, you should discontinue water changes for 8 to 10 days, everything else can continue as usual. Disadvantage: This works great with tanks that are new, and in the process to establish their balance. For other tanks, sometimes this doesn't work. Also, it takes some patience, and the first days the GW actually can get thicker.

2) Blackout. Cover the tank for 4 days. Before and after you need to do water changes, because the dying GW organisms possibly increase NH4 levels, while plants -- in the dark -- won't be helping much to take them up. Disadvantage: This doesn't battle the source of the problem, so a week after you uncover the tank you might be greeted by pea soup again.

3) UV sterilizer. Works great to kill them. Need to keep an eye on NH4 levels, do water changes, clean filters, etc to avoid buildup of dead matter. Disadvantage: costs some money, and since we are fighting the results of some imbalance, we need to repeat treatment as necessary, or let it run all the time.

4) Diatom filtration. Diatomaceous earth contains tiny little shells of tiny little critters. Send dirty water through it, all the dirt, including GW, remains stuck in the diatoms. Disadvantage: Costs some money, can get a little messy if you are not careful, and might need repeated treatment.

5) Daphnias and other little crustaceans live off GW. Problem is that in the food chain, fish live off Daphnias, so you'd need to separate the two somehow. Disadvantage: I have never heard that this actually worked. It would be great to have a second tank full of daphnia which clean the water of your show tank, and once in a while you scoop some of the little critters over to feed your fish.

That should get you started!
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post #3 of 7 (permalink) Old 07-11-2004, 12:02 AM
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Even at 5ppm your PO4 level is pretty high. It's usually recommended that NO3 to PO4 be 10:1. With your light levels you may want to try for NO3 level of 5ppm and .5ppm of PO4. So you may need to continue doing some large water changes until the plants can catch up.

The mechanical methods that Wasserpest mentions will clear up the tank for a time, but unless you get to the root of the problem the GW will return.

Good luck.

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post #4 of 7 (permalink) Old 07-11-2004, 07:11 PM
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Since you keep Discus, you might want to consider investing into an UV sterilizer anyway... keeps the water low in germs, Discus might like that...
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post #5 of 7 (permalink) Old 07-11-2004, 07:25 PM Thread Starter
Algae Grower
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Location: Scotland, UK
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Unfortunately I just sold my UV steriliser on ebay. Used it on my marine tank and hadn't needed it for over a year. So I won't be buying another.

Will try to get the PO4 down to <1ppm by doing increased water changes. Have given the cannisters a clean and a good gravel vac. Hopefully will decrease the nutrients. I think I will wait it out. The tank has looked like crap for months now so another few weeks won't hurt.

Should I continue with the plant food or leave it til the water clears up? I have read that in order for the PO4 to be used by the plants all the other nutrients need to be there or will this fuel the algal bloom?

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post #6 of 7 (permalink) Old 07-11-2004, 07:56 PM
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Not sure about your PMDD mixture, but I would keep the NO3 from bottoming out, that is, add KNO3 if it goes below 5 ppm.

BTW, this is the first time that I heard of PO4 levels over 30 ppm in a fish tank. Must have been an amazing amount of buffer in there. The test kit I am using goes only up to 2 ppm
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post #7 of 7 (permalink) Old 07-11-2004, 09:28 PM Thread Starter
Algae Grower
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Location: Scotland, UK
Posts: 22
My test kit only goes to 3ppm but I did a 1/10 dilution using phosphate free RO water. I used Waterlife's pH 6.5 buffer as I was having probs with high pH upsetting the Discus. The buffer is phosphate based and shot the levels through the roof. You live and learn.

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