Green water - Algae bloom

Green water (algae bloom) Beautifully made photo by Ron© .
This is the most common problem if the cloudy situation extends beyond 10-14 days. Note that "green water" is not always green in appearance! Since green water is the most common problem and the most difficult to solve the answer needs to reflect several options. The situation that causes GW (Green Water) is usually a combination of high nitrates, phosphates, and mixed in some ammonia/ammonium. Substrate disturbance is usually the culprit. What happens is the algae (GW form) will flourish off of the ammonia/ammonium and phosphate, remembering that algae can consume phosphate easier than plants because of their thin cell walls, the algae uses up the ammonia/ammonium and phosphate, but it doesn't go away...because algae can quickly switch with nutrient it scavenges...it moves to nitrates. So you can see why water changes will not rid a tank of GW. Nutrients can be reduced very low in GW and fairly quickly by the GW algaes, but they can scavenge other nutrients...iron and trace elements. So, it's very common for the GW to solve the situation that causes it to begin with, but that won't eliminate the GW, for the reasons I've allude to. Five methods exist to eliminate GW. Blackout, Diatom Filtering, UV Sterilization, Live Daphnia, and Chemical algaecides/flocculents. The first four cause no harm to fish, the fifth one does.
Method No. 1 The blackout means covering the tank for 4 days, no light whatsoever is allowed into the tank during this time. Cover the tank completely with blankets or black plastic trash bags. Be prepared, killing the algae will result in dead decaying algae that will decompose and pollute the water. Water changes are needed at the beginning and end of the blackout time and ammonia should be monitored also.
Method No. 2 Diatom filters can usually be rented from your LFS. This is my preferred method. Personally, I use my Magnum 350 w/Micron Cartridge coated with diatom powder. Diatom filtering removes the algae and doesn't allow it to decay in the tank. You do have to check the filter often, if you have a really bad case of GW the filter can clog pretty quick. Just clean it and start it up again. Crystal clear water usually takes from a few minutes to a couple of hours.
Method No. 3 UV Sterilizers will kill free floating algaes. They also kill free floating parasites and bacteria. They also can be problematic for extended use in a planted tank, as they will cause the “breakdown” of some important nutrients. They are expensive and don't remove the decaying material from the tank, if you can afford to keep one they are handy to have around, though not as useful IMO as a diatom filter.
Method No. 4 Adding live daphnia to your tank. This can be a bit tricky. First you need to insure that you are not adding other "pests" along with the daphnia. Second, unless you can separate the daphnia from the fish, the fish will likely consume the daphnia before the daphnia can consume all the green water.
Method No. 5 I hate the last way, the flocculents stick to the gills of fish, while not killing them it does compromise their gill function for quite a while leaving them open for other maladies.
Beautifully written article by Steve Hampton© ; more on Aquarium Plants.com

"Green Water - Dusko's Lazy Solution to the Problem"
Photo credit Dusko Bojic

I got a very bad algae bloom (Green Water) due to CO2 malfunctioning ( + 2 of my HOBs malfunctioning also). At first I wasn't sure what to do. I had very little free time and such Green Water case needed many water changes and adjustments.
I decided to try something new!!! Instead of the everyday water changes and fuss I decided to introduce LOTS of floating plants, almost covering all the water surface. I got Salvinia natans floating plant. I disconnected the CO2.
Since "green water algae" thrive in water with NH4 and strong lights, I planned to add floating plants to shade the tank (something like black-out) and to uptake the NH4 from the water column.
I also started dosing Easy Life FFM (fluid filter medium) in USA aka Easy Neo. This fluid product has a very good CEC (cation exchange capacity) and is able to bind NH4 very fast. I dosed Easy Life FFM every second day (recommended is once a month).

This next photo was taken approx 10 days after I had introduced the floating plants and Easy Life. Amazing!! And I didn't do any water change at all !!

Today this aquarium looks like this (following photos). I disconnected the CO2 and am running this tank as a Hi-light Low-tech covered with floating plants. The submersed plants seem not to mind these unusual conditions without CO2. I do dose Tropica+NPK 10ml every week. Instead of water change I only top up the evaporated water and re-dose with 10ml of Easy Life. Today I have no algae at all and plants which grow healthy.