Algae attack and Fish are now dying

We have an urgent situation now. I am new to salt water aquariums and an algae problem has gotten way out of hand fairly quickly. An now I have lost a shrimp and a yellow tang in less than 30 hours.

I have tested the water with the following results:
Ammonia = 0
Nitrites <0.3
KH = 6
PH = 7.5/6

I think there is a chance that it is possible that the algae is taking O2 out of the water and that is suffocating the fish. Don't know.

What I have done so far is:

1. clean the skimmer (was clean last week but now was clogged with algae)
2. clean the BRS (carbon and GFO)
3. put a temporary air pump and bubble stone in to add O2.
4. a 20% water change

I think my problem is that we have been topping off with RO water (but it is not DI). And we may have been overfeeding a bit (half a cube of frozen shrimp every 3 days and some tropical flakes daily). Lights are on 8 hours per day on a timer.

The tank was up and running for a year and a half and we moved it (took everything out and cleaned the tank and put it all back including almost every drop of water) about a month and a half ago.

My questions:

1. What can I do to save the rest of my fish? Urgent steps I need to take but haven't? I have an empty tank, start a temporary for the fish??
2. How do I keep this from happening again? How do I kill off all this algae? What type is this?

Thank you all for your help!

 

You should definitely bring up your pH. I don't know if that's what's killing your livestock, though :-/ What size tank do you have?

 

It's a 50gal.

 

The Yellow Tang might have died due to stress being in a tank that size. They need tanks of 90+ gallons. I'm not sure if that's the cause of the death of the Tang, and it probably has nothing to do with the death of the shrimp, so I'll let someone else chime in.

 

im pretty sure that algae adds O2 to the water. You shouldn't register any nitrites. Have you added anything to cause a mini cycle? I would probably blame your water quality for the deaths and the algae. What are your nitrates? Do you have a clean up crew? What fish do you have in there now?

I noticed you said "clean the carbon and GFO". How old is it. it might need to be replaced.....or is that what you meant?

 

when you say took everything out, what did you do with your sand?

 

That's a very good question.

 

Your alk is also pretty low, that could be causing the ph to be low too. Could be a cycle if you are reading nitrites. Most likely the algae is sucking any nitrates out of your water so they may be testing low to nothing. If you think stress from yellow being in a small tank(Dont look at pic 3 and see the blue regal tang in there as well) More stress?
I would get more carbon and a turkey baster and start blasting that sludge off your stuff, sklim wet and get some water changes ready. Also with your ph so low what is your salinty at?

 

I think your tank cycled again after the move. From which your algae problem has occured. There was probably an ammonia spike followed by a nitrite spike and of course nitrate and bam theres your dead fish and algae. The sand also contains toxic junk which is why stirring it up during cleaning is not good. In the last few years ive had to major moves ( one was an actual move and the other had to replace a 16 yr old 90g. During the first move a couple years ago i used the same sand/argonite and exactly 21 days later the tank crashed and i lost almost everyrhing. I replaced my 90 6 months ago and this time i replaced sand with new stuff and basically treated it like a brand new tank ( cycle wise). I doubt the algae has caused your problems but is rather the symptom of something else ie mini cycle, extremely high trates etc..get yourself some dr tims or other bio kickstarter and do a series of water changes. Im guessing your nitrates are high. The worst of it is probably over but theres no harm in treating the tank like it is brand new and cycling. If you have to replace the sand just keep a cup or two of the old to reseed the new stuff.

 

Could be a dinoflagellate bloom. They can release toxins which are harmful to fish or inverts. There is also the oxygen depletion factor. As bacteria break down all the excess organic material, they consume oxygen.

Is there anything you can do to get RODI water? Or at least test the water to see what the phosphate levels are?