Cloudy water, fish dying

Question
I had a freshwater tank for about 1 1/4 years (about two months since I added the last fish) and the water suddenly went green. At first I thought it was the tank cycling so I let it resolve itself. I soon found that it was algae and I added an algae remover. Not long after that fish started to die. First it was four guppies and two zebra danios. I went to the LFS and they suggested parasites. I bought the bottle of parasite medicine. A week later the remaining two danios died along with a swordtail. Then about two weeks passed and one gourami died. By this time I had finished the bottle of parasite medicine. I had taken the carbon out of the filter during this time. Two weeks later the other gourami and an otto died. Now I only had three black tetras. The algae problem had still not gone away. I decided to put the three tetras in a separate tank (where they are still alive and happy today) and totally clean the entire tank. I siphoned out 100% of the water and I cleaned the gravel. I used a toothbrush and scrubbed the plastic plants. I also let them sit for a few days to dry. I moved the biological filtration into a 20 gallon tank half filled with the original aqurium water. I also put into this tank an unknown live plant of some sorts. I replaced the bio filtration which had been sitting in the half filled twenty gallon tank for two weeks. (It took me a while to add all the water) I replaced all filter pads and charcoal with new ones. I then scraped down the walls of the tank with my algae sponge and reassembled the tank. Three days later I went out and bought 8 neon tetras thinking that it would be safe to add them because I had saved the bio filtration. Apparently not, three days later 7 died. The water was getting cloudy again.(I added algae destoyer the day before they died, coincedence?) I went to the LFS with a water sample a week and a half later so they could test it. They said it was safe to add fish again(0 ammonia, nitites; not sure on nitrates) I bought another five neons to accompany the remaining one and a bannana plant. Now, over a week later, everybody is still alive and happy but the water is still cloudy. What is happening? It is a 26 gallon tank with Ph of about 6.7. Also I use RO water with a PH of 6.3: how does it get more alkaline in the tank? I do about 7-8 gallon water changes every other week.

Answer
Hi Pat
Are you using 100 % RO water?  Or are you mixing it with tap water as well?

Don't use the algae remover anymore.  They don't work-they're not addressing the source of the problem.  Another problem with using them, they have a tendency to deplete the oxygen in the water, especially if the water is kept at a higher temperature-78F +.  Warmer water also depletes the oxygen, so the combination of the two can be deadly to fish.  If I had to guess, from what you've said, I would say that may be what caused the fish deaths.  Any medicines in the tank-for parasites or bacterial infections is also stressful to the fish.  So it's usually not recommended to treat for something unless you're fairly certain that's what the problem is.  Personally, I would start searching online for information before listening to the LFS, I have no idea how they came up with parasites as the problem.  There are some good stores and good employees, but there's too many out there that really don't know a thing about fish.  

The algae problem....that's a classic algae bloom.  It's a free floating algae what's causing the green water.  My checklist of things to check,
how long are you leaving the light on?  Should be no more then 8 hours with no live plants, and no more then 10-12 with live plants.
 
Is the tank receiving direct sunlight?  If so, put some curtains on the window, or move the tank.

How often are water changes being done?  You said every 2 weeks...I recommend with a normal stocked tank, changing out about 25% of the water once a week, and being sure to vacuum the gravel/substrate good.

Is the tank overstocked?  Too many fish, combined with not enough water changes will make the nitrates skyrocket-possibly causing an algae bloom.

Are the fish being overfed?  Same as above, too many nitrates and phosphates added to the tank just feeds the algae.  I recommend only feeding once a day, what the fish will eat in about 5 minutes.  Scoop out any remaining food.

What kind of filter are you using?  Meaning gallons per hour(gph) output, for a 26 gallon tank, you'll want a filter that will put out a minimum 260 gph.  I usually recommend going higher then the minimum, and for some fish even doubling that number for filtration.  Do a search online for your brand and model of filter-or let me know what it is I can find it, most sites will mention what the gph output is.  Another thing you can do, leave the water line down a tad from the filter output-that will help churn/agitate the water surface-allowing the water to get oxygenated and releasing the CO2 from the water.

I've heard live plants can help as well-though shouldn't be in place of frequent changes.  Java moss and java fern are supposed to be really good to help with a nitrate problem.  

I've never tried this, but have heard it worked for others-it's called a total blackout.  Completely cover the tank with a blanket/towel, so no light gets in.  Make sure the light doesn't turn on.  Leave it like that for 3-4 days, zero light, no peeking!  No feeding the fish-they'll be fine, they can go a few weeks without eating.  Plus, they'll have some algae to munch on if they get hungry :)  The lack of light is supposed to kill off the algae, because even 1 small speck of light will be enough for algae to grow.  Do a good thorough water change, and following the above info should take care of it.

Hope that helps, and good luck with your algae control!  Let me know on that RO water...

Christy