Help with mysterious fish deaths ?

[Hemisunshine]

I’m not quite new to the hobby but I’m not a seasoned vet either. I’ve had a 40 gallon going for two years, started at low end brackish, and bumped up very slowly over these past couple years until I am now at 1.021 specific gravity. just recently moved all the decor and substrate over to my new 75(sand substrate, both canister filters, all decor, everything from the old Tank swapped over) new tank was set up for 2 months And one morning the light came on and I had 3 dead mollies and one dying. Now this week I had two firefish Goby’s die overnight. None of them show any signs of being beat up or damaged from other tank inhabitants. And all of these fish seemed totally fine the day before their deaths, no signs of heavy breathing or odd behavior or diet issues. All water parameters are the same as they’ve always been since the tank cycled 2 yers ago. 0 ammonia, 0 nitrite, about 40-60 nitrates (my well water comes out of the faucet at 40 ppm on nitrates) ph is about 7.8-8.0 temp always steady at 80.5 degrees. I know mollies aren’t saltwater but they were bumped up very slowly and it just strikes me odd they would all parish in just one night. I had 5, now I’m down to 1 and he is doing just fine, as with the firefish I had 4 now I’m down to 1. Other tank mates are a green spot puffer, figure 8 puffer, blue neon puffer, 2 small snowflake eels, 2 bumblebee gobies, 2 ocellaris clownfish, a black clown goby, and a handful of red/blue leg hermit crabs. I’ve got probably 20lbs of live rock, feather duster worm and a condylactis anemone as well. Tank is 75 gal with two 315gph canister filters hooked to two spray bars. Water changes weekly at 10-15 gal mixed with instant ocean salt, and always seachem prime added. I’m just wondering what could cause sudden fish death like this when the fish all were behaving completely normal the previous night, and when all water parameters are within reason. I do not test for dkh

[JustinM]

That seems to be a lot of fish for a 75 gallon tank with very little flow. Is there any surface agitation to help with oxygen exchange? You also have quite a few puffers, any chance they released any toxin?

[JustinM]

By the way, Welcome to Reef Central!

[Hemisunshine]

Yep today is my first day here, as far as surface agitation my two spray bars run the entire length of the back of the tank, and disturb the entire surface. But I also have quite a large air pump with stone disc for added aeration. I surprisingly don't get any salt creep that I notice so the bubble disc works well for me. It is a few puffers indeed but the blue neon is new to the tanks, and the issues I had were before I added him. All puffers and other livestock are very young and small yet so nobody it too overcrowded i don't think. As far as toxins I am not sure if the puffers I have even have any, I couldn't find anything in my research (I always do extensive research about each fish before add them) the only thing that would be a big coincidence is that the night before I lost all the mollies I had stirred up the tank pretty food trying to get a purple pseudo out that was causing everyone problems and I've heard about dangerous substrate glasses or pockets of ammonia but I 'll still unsure if the events are related

[JustinM]

Your nitrates are beyond high! I didn’t even catch that the first time. Even at 40, that is bad. I would invest in a RO/DI sooner than later. I would start with that. Where in PA are you, if you’re in or around York, I can give you as much water as you need.

I’m not saying the nitrates killed your fish but it will start causing stress. Have you double checked your ammonia? Are there any symptoms before the fish die(heavy breathing, swimming into the flow, hiding) let us know anything.

[JustinM]

If your sand bed was never disturbed and you stirred it up, it can cause mini cycles. This is possibly what happened.

[Hemisunshine]

Well it was disturbed when I initially moved the sand from the 40 to the 75 but it went about 2 months without being disturbed until that day, then it got disturbed at about 730 at night and then I went to bed and woke up with 4 dead fish that morning. About a week after that I’m having insane brown algae outbreaks for the first time ever in two years. I thought about a protein skimmer for getting rid of waste to reduce nitrates but I think the RO water may be better option. My dad has a 120 gallon freshwater and has kept fish for his whole life but never saltwater, I’ve mentioned to him about needing to use rodI water because our tap water has high nitrates but he didn’t think nitrates were that big of a deal to worry about, but from what I read online corals and anemone think they are a big deal. But yeah they have been 40 or higher since day one, as my fresh well water out of our sink comes out at 40ppm

[Hemisunshine]

I definitely appreciate all the input as well, I’m in montorsville PA and there are no good LFS’S around to ask for help and this is my first time joining a forum

[Jdub968]

All fish looked good the night before ? I have the ?'s justinm asked about breathing flashing also clamped fins? It's possible stirring up the sand got something in the water colum. Firefish and mollies are all pretty hardy fish

[Hemisunshine]

Yep all fish were fine the night before no clamped fins no heavy breathing, no odd behavior and all ate fine. I’ve heard mollies and firefish are hardy...which is what’s got me so stumped because puffers are notoriously finicky and need pristine water conditions, and yet all the puffers remained totally fine, but the supposed more "hardy" fish in the aquarium were all but whiped out completely (one mollie remains alive still) in fact i just got a replacement firefish last week, and put him in about 5 pm, and he was doing great, and found him the next morning dead on the bottom, but untouched as well(no signs of him being picked on)

[Jdub968]

I think if it were me I would hold off on other fish purchases and watch the remaining fish closely keep an eye out for heavy breathing scratching flashing clamp fins lethargic behavior breathing at the surface ect. Do another water parameters check look close at ammonia. Also did you by chance do a WC before the deaths say with in 24 hrs or so? Well water parameters can fluctuate drastically from day to day week to week causing huge ph swings hardness and alkaline fluctuations that can cause osmotic shock.

[Hemisunshine]

I didn’t change water the night before, just stirred up the sand quite a bit trying to catch the pseudo. But when I woke u-with the 4 dead mollies I did a 15 gal water change. I do water changes every week always 10 gal. I’ve been testing every day since that incident about 3 weeks ago, ammonia and nitrite always at zero, nitrate was high but always has been, and now is actually coming down(was 60, now at 40 or 30) I suspect because of adding my matrix into the canister. Ph was at 7.8 but has came up to 8.0 now in the last few days(always check at same time of day as well) temp always constant at 80. I’m definitely holding off on adding anything new until I get his figured out. That firefish I mentioned was bought Monday mid day and was dead when the lights came on at 9 Tuesday morn. But he ate great the night I put him in and when I woke to find him dead I checked my levels and got the same readings I’ve been getting

[Hemisunshine]

That’s yet another reason I’m coming to the forums is because the fish show absolutely no signs of stress or any parasite or illness, they’re seeming just dropping dead.