Can't keep new fish alive - What am I doing wrong???


Reefing newb
Hi All,

I'm trying to figure out why I have such poor success keeping new fish alive. My knowledge level is decent, but there's plenty I don't know and I'm always trying to learn more. Please tell me what I'm doing wrong!

I have a 125gal FOWLR tank that's been running for about 5 years (only 4 med/small fish the last 2 years so not much bio load). For water changes I use water from my 5 stage RO/DI filter and mix with Instant ocean salt for about a day before using. The LFS says my water is good, and I follow slow acclimation process of replacing a small amount of LFS bag water with water from my tank over the course of 1-1.5hrs.

This last time around I used an 20gal isolation tank (with a big skimmer, live rock, & 50% from my established tank) and still couldn't keep a few fish alive. I had two butterflys (Auriga & Copperband) and two dwarf angels (pygmy & Tibicen). Only the pygmy is still alive. They all ate well except the copperband. The copperband got some disease where he had cotton like growths on him, and the Auriga got open wounds on his body a week later (pics below). I treated the 20gal tank with API Furan-2 with no luck (fish died before full treatment could be applied). The pygmy is alive and well. I have a wide variety of food that i try to coat with Seachem Garlic Guard to get the fish to eat. I usually give them a mix of plankton, bloodworms, mysis, krill, brine, fish eggs then the usual flakes and pellet.

Should I just always use copper in my isolation tank just to kill off any diseases with new fish? My LFS said if I really wanted to I could put copper in my 125g tank but that everything but the fish would die. I'm not sure I want that route just yet (seems like a last resort).

My equipment:
Tons of live rock & crushed coral
Big Sump with bioballs & more live rock in sump
Big Protein Skimmer
UV Sterilizer
3 Hydor Koralia 1 Powerheads
72" Coralive CF Lighting with 12k bulbs
RedSea Merlin 120 Fluidized bio chem filter (got this from a friend recently and haven't used it yet. Not exactly sure what it does)




Are you putting them into the QT tank one at a time or multiple in the tank at a time?

Also just keeping a butterfly in a 20 gal is enough to stress them to death because that is much too small. They are such a challenge to keep in a correctly sized tank that adding the stress of a small space is something i think many wouldnt be able to handle.

What are your water parameters at? It looks like your tank is covered in cyano which indicated poor water quality and for the fish you tried, can be a death sentence.
You've got very difficult fish choices there. Cooperbands, especially, are hard to keep.

You definitely need to post actual numbers for your parameters - ammonia, nitrites, nitrates, phosphates, ph, temp, salinity, etc. Are you getting the fish from the same place? If so, maybe it's time to change and find a more reputable lfs.

I've never qt'd my fish, and have only lost maybe 4 fish out of the many i've purchased over time. Not to say you shouldn't qt (I wish I HAD qt'd all my fish)...but when you qt your fish, and you put them back in the tank that already has fish, they'll get whatever parasite the tank already has anyway. You'd have to keep your tank fallow (fishlesss) for a good 3-4 months to ensure the death of parasites, then qt all the fish.

Don't ever put copper in your dt. Once you do, you'll pretty much never be able to keep any type of invert in there (or at least not for a very long long long time). Copper seeps into everything, including the silicone, and inverts have zero tolerance for copper.

I see you have you clean it regularly? They're really not good for saltwater unless you rinse them out in saltwater regularly. If you want to ditch them, you can do so, 1 cup at a time over a period of a few weeks..
On top of everything everyone else has mentioned, you may have an unknown predator in your tank taking your fish out.
+1 LF, That cyano looks bad. I would get rid of your bio balls, try and increase flow and get in there and yank some of that cyano off.
Hi All,

So I tested my water today and temp is 78 degrees, Amonia & Nitrite are 0 ppm. Nitrate is about 15ppm. SG is 1.016 (I hear a lower SG helps keep sickness away). What affect does a low SG have on fish long term? Don't have a pH kit but I've heard with that much crushed coral and water changes you should be okay (I'll get a pH kit now).

The general consensus is I have too much algae, and i need to check my water quality more. I have a few ideas I wanted to share.

1) Would something like a "2 little fishes phosban phosphate reactor" do any good for me? I can get one for about $35.

2) The way I have my rock set up is that I put the nicer more decorative/fragile pieces on top of the stronger more solid rock. This means I never really get my siphon hose under that rock when doing water changes. I'm only vacuuming the front half of the tank. Maybe another arrangement that lets me vacuum more floor space is better and worth trying? Is that significant?

Thanks for all your help!
Hi chichimom79,

I posted my water results above. The top is open air. Does that matter?

That is a good thing. Just keep up with your evaporation. The depressed salinity should be fixed. Not sure what effects it has long term but I know it can't be good. Aim for 1.024SG
Increase your flow also. You will get less detritus buildup in your rock and sand.
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Open air is better for your system than running a cover.

I have a few thoughts on your situation that may help

1. Cyanobacteria - It's everywhere, you really need to get this figured out. In large concentrations I believe it can be poisonous to fish and corals (definitely corals - I learned that first hand when I had cyano issues). Your nitrates are fine, but I am guessing you have a phosphates issue. You mentioned a phosban reactor, and yes, running one of those with GFO will help lower phosphates. Your nitrates are testing low, but thats likely because the cyano is consuming nitrates out of the water column. Bio balls are usually a nitrate trap, I would try to replace those with crushed live rock and some macro algae if possible (I dont recall the specifics of your sump). Also, are you using RO/DI water or tap water? What are you feeding, and how often?

2. Fish Choice - I noticed you had issues keeping butterflies alive. This is because pretty much every butterfly available to us are very difficult to keep. Most of them eat coral for at least some of their diet, making them hard to feed in captivity (or expensive, if you have a fully stocked reef tank)

3. QT - I noticed you had rock and sand in your QT, this kind of defeats the purpose of the QT. You don't want rock or sand in it because that's where all the little critters that cause issues for fish live. You want the QT to be as sterile as possible, you can use a small HOB filter for it (along with frequent water changes). To give the fish some cover, get a few pieces of properly sized PVC pipe and place them in the tank.

4. Salinity - While your tank looks to be fish only, I think a salinity of 1.016 is far too low, I would bring that closer to 1.020 or 1.021, but I am sure others will chime in on that
+1 Angie

I would also replace your crushed coral with sand (crushed coral can become a nitrate factory), get yourself a good test kit (check out API or SeaChem), and get yourself a refractometer to measure salinity/specific gravity (not sure what you are using now but hydrometers are inaccurate and need to replaced regularly, easily paying for a refractometer in no time!)

If you do raise your salinity, which you need to do, make sure to raise it SLOWLY - I think the rate is around .001 per day, but check out some other recent threads that talk about salinity.

Last piece of advice is to get some easier fish - the ones that aren't making it are notoriously impossible to keep alive even for the best reefers!
+1 about SG. That needs to come up. Right now, you are actually in the brackish range (1.007-1.017) So your fish are definitely getting stressed. The low end for a SW tank should be 1.020. You can dip down into the 1.019 range to treat fish but I would only do that in your QT tank. Fish are pretty sensitive to SG for some reason but the more stable you can keep that parameter, the happy your fish will be.
+1 Everyone

I would also add that crushed coral doesnt work as a buffer. I have no idea where that rumor got started, but for the agronite to start being dissolved the pH has be lower than 7 which would definitely kill your fish. You are much better off with regular sand.

Your solutions to these problems are going to be replacing the crushed coral, getting your salinity up, and water changes, water changes, water changes, water changes!

I would also stop trying to QT your fish unless you are going to invest in a bigger setup and do it properly. Leave you main tank fishless for 3 or so months and treat everyone you get after that. Most of us dont QT our fish. Fish that arent stressed hardly ever break out in disease and can live long healthy lives in our tanks. And considering how easy it is to create a stress free enviorment (dont over stock, feed good food, choose correct fish for the size tank you have, good tankmates and good water quality), its the route most of us choose to follow.