Hi,
Unfortunately this morning I lost half of my fish in my 90 gal.
my main concern is how to treat the tank so I can put the other half back in.
Last night my tank was crystal clear, and this morning it was cloudy and white. I did all of my tests and the only thing that appeared slightly high was nitrites (1-2ppm)

My tank did not become too warm overnight as to fry my fish, My filter is still working fine, The tank is well established and cycled, I did a 50% water change a week ago

I already consulted 3 people who I believe are more knowledgeable about fish than I in my area - none of them had any clue what my problem is.

My thoughts are that this could be caused by 3 things :

Algae that removed all the Dissolved Oxygen and then died (but this happening overnight in a 90 gal in unlikely)

Some kind of bacteria in the tank - if this was the case do I need to take everything out and sterilize it?

A chemical somehow made it's way into the tank (I haven't added anything to the tank since I fertilized 2 days ago (today was supposed to be fert. day)

R.I.P. - 2 bala's (Dos and bala) 1 electric yellow cichlid(bannana fish) 1 german blue, and 2 pictus catfish

Thanks,
Nerb

Is overfeeding a problem for you? That could gradually build up decaying food in the substrate, causing a bacterial bloom. Do you use CO2? DIY CO2 can sometimes get too much yeast in the tank. Pressurized CO2 can sometimes get to too high a concentration. One dead fish, not noticed by you can cause a massive bacteria bloom if the fish is big enough.

thanks for your responce Vaughn!
I feed what they can eat in 3 minutes (usually there isn't any left) I have a diy co2, but it is rare to get any of that liquid into the tank (the tubing is always dry and still was this morning). I couldn't find one fish last night, but it was a tiny one.

I did a 50% water change, and the water is about 50% as clear as it was before (still pretty cloudy) should I try a water clarifier? I was just noticing that even my plants are starting to look upset now. I think if everything is still bad tommorow, it might be time to take EVERYTHING out and wash/disinfect. - this means I will have to cycle again if I cleaned out my canister too

I actually have pictures from yesterday compared to today if anyone would like to see them and I could take a current picture (maybe even some closeups of the plants)

strange to see a perfectly fine tank flip around in one night.

any plumbing work in your house lately? any pH adjuster?

I only mention that because those where 2 troubles I had about a year ago and copper did kill many IFGA guppies ! and the ph because I had a problem once when I used to be very concern at keeping them an 7.5 pH and the water turn cloudy.

no recent plumbing, I use seachem acid buffer about once a week (I have some 'found' rocks that would love my water to have a ph of 8.0)

There is one major problem you are making. Using acid buffer is virtually always a major mistake in a planted tank. You might possibly be right to use it in some circumstances in a fish only tank, when your water is very hard, but I can't think of a situation where it would be beneficial in a planted tank.

The "found" rocks you have are dissolving in the water, increasing the KH and GH, and making the pH of the water go up. As you continue to add acid buffer in an attempt to keep the pH lower you are just increasing the total dissolved solids content of the water, filling the water with unneeded ions. Eventually that will kill the fish, and may have done so for you.

I didn't know acid buffer was bad. when I started using it, my plants seemed to notice the difference. (don't my plants and most freshwater fish become unhealthy in a pH of 8.0?)

The acid buffer I use says its designed for planted tanks and converts KH to CO2(is that the releasing ion part?) - strange to think it will kill fish. I only usually add it on water change days. So should I stop using it all together and live with really high pH?) (I can't afford a RO or to buy RO water from the store every time i need to refill)

anyway - my water is still very cloudy. Does anyone think that I could use alum to flock the particles since there is no fish in there? aluminum sulfate is a common additive to drinking water treatment, and also used to remove algae or snails (I forgot which one) on plants - people soak their plants for days with this stuff (so it must be safe for plants too) or should I use a clarification product from pet-co/smart that says safe for plants?

or should I continue daily 50% water changes until it is gone?

Thanks so much!
-Nerb

following Vaughn's line... I have hard water in my house . If I only add tap water to my tanks the ph will climb up to 8 in a few days. Everytime I do a water change I add a few gallons of RO water.

would 5 gal be enough ro water for a 50% water change on a 90 gal tank?

so.. 90 gal minus dirt rocks and plants is prob. 70 actual gal.. 35 gal is a 50% WC.. that makes 5 gals - 14% of the water added. maybe 10 gal/30% of RO added to the water changed would be more appropriate.. it would only cost... $2.50 a water change for 10 gal of RO water from the machine. would I need to add anything like gh booster or baking soda and trace if I did this?

Thanks,
Nerb

If you add RO water to reduce the hardness of the water you shouldn't be adding anything to bring the hardness back up. One thing to do is try to find out if there is enough magnesium in your tap water. Some, if not most, water companies provide yearly water quality reports that include magnesium ppm. If there isn't any or just a trace of magnesium, you can add some epsom salts to get enough in the water.

It would probably be best for you to just ignore the pH of the water. GH is good for plants and fish, so ignoring that is a good idea. Water companies add something, usually phosphates, to the water to raise the pH above 7 so copper piping is not eroded by the water. By ignoring pH entirely the worst that happens is that your plants don't do quite as well as they could do, while attempting to regulate pH seems to have caused you to lose your fish. I would prefer somewhat slower growing plants to losing fish.