Help Please! I messed up..

[spencerkilgore]

Hey everyone — I’m looking for some guidance or opinions on what may have caused the sudden loss of my cardinalfish in my 20g reef tank. This was my first fish loss, and I’m trying to learn from it so it doesn’t happen again.

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Tank Overview (Pre-Incident Setup):​

• 20g saltwater tank, running for 38 days, fully cycled
• Stock: pair of clownfish (still doing fine), a couple of crabs/snails, macroalgae, and 1 cardinalfish (the one who passed)
• Filter: TARARIUM Aquarium Filter with UV, live rock, live sand, and filter floss
• Flow: Powerhead runs 8 am–8 pm, off overnight; HOB filter runs continuously for surface agitation
• Dosing: Microbacter7 + Microbacter Clean daily
• Recent Additions: 1 jar of copepods and a bottle-recommended dose of phytoplankton (added at night)
• Parameters (day before incident): Ammonia 0 | Nitrite 0 | Nitrate 0 (strip test)

What Changed:​

The TARARIUM filter (fully submerged) was a hassle to clean — every time I removed it to change floss, it dumped a bunch of gunk into the tank. I use a Seachem Tidal on my 75g and love it, so I decided to swap the 20g over to one as well.

I rinsed the new Tidal with RODI, transferred the filter mesh from the old filter into the new one (to preserve bacteria), and let it run for a few hours before testing.

Results came back with elevated nitrite (~1+) and rising nitrate.

Chain of Events:​

• I performed a 20% water change and dosed AmGuard (before realizing Prime was better for nitrite)
• Ordered Prime immediately — it didn’t arrive until the next day
• That night, my cardinalfish began breathing heavily and became lethargic
• I performed another emergency water change, but during the process realized my reservoir heater malfunctioned, and the replacement water was 84°F
• Switched to another reservoir and completed the change slowly to avoid shocking the fish again
• Despite efforts, the cardinalfish passed overnight
• The next day, I dosed Prime; the clowns appeared fine
• However, I lost 2 snails and 1 red hermit crab that same night

Biofilm Explosion:​

Around this time, I also experienced a major biofilm bloom — it’s coating my glass, powerheads, sandbed, and macroalgae. I assume the combination of:

• Filter change (bacteria disruption)
• Copepods + phyto dosing
• Reduced nighttime flow
• Overfeeding the week prior

…led to this full-blown ugly phase massacre. The water has been cloudy since and smells “reef-soupy,” but not rotten. I added filter floss recently and it's starting to help.

• What, in your opinion, was the tipping point in this chain that pushed the system too far?
• Should I be doing something different for nighttime flow?
• Any advice for biofilm management during this early ugly phase? I want to keep pods thriving, so I’m not running UV anymore, plus I no longer have a UV on the tank.

I’m not trying to deflect responsibility here — I know I made a few mistakes and rushed some changes — but I’m hoping to understand what led to the cascade. This was my first fish loss, and it hit me harder than I expected.

Any insight, tough love, or advice would be appreciated.

 

[Tahoe61]

In a nut shell the tank is not fully cycled yet. Over feeding probably overwhelmed the biological filter.
You're adding too much product to such a young tank. Stop the Microbactor7 and Microbacter Clean dosing. Prime is not going to fix the problem.
Get an ammonia badge, feed sparingly. Don't turn off the flow at night, that's just decreasing oxygenation at a time when oxygenation is already decreased.
You're off to a good start, but limitations like HOB filtration leaves little room for error on a new tank. Just slow down and let the tank do it's thing.



:)

 

[redseaenroute]

Honestly... It sounds like a case of over reaction. Not trying to be rude. But changing equipment, plus elevated temp, plus addition of Amguard and prime, plus microbacteria 7, plus microbacteria clean, plus water changes, plus flow changes... This may have just been to much for the fish to handle in such a short period of time. Could be lack of oxygen as well, with a bloom comes reduced oxygen.

This tank is still very very new. My advice would be to let things settle....As long as your salinity is correct and stable, your temp is correct and stable and you have flow, you really shouldn't have to add or do anything else for a few months outside of feeding and scraping glass. Don't add anymore bottles of anything at this point. Continue testing and monitor. Let the tank settle in. And don't add any more livestock in that time.

 

[Mr. Mojo Rising]

Agree with above comments, especially the flow, there's very little movement in your tank, point that powerhead at the surface and let it run 24/7.

Get good test kits, the strips are useless. Don't get API, get salifert.

 

[Pistondog]

I think there was a bacteria bloom, reducing oxygen to dangerous levels.
I run an air stone in my aio.
Keep the powerhead running all the time.

 

[redseaenroute]

In a nut shell the tank is not fully cycled yet. Over feeding probably overwhelmed the biological filter.
You're adding too much product to such a young tank. Stop the Microbactor7 and Microbacter Clean dosing. Prime is not going to fix the problem.
Get an ammonia badge, feed sparingly. Don't turn off the flow at night, that's just decreasing oxygenation at a time when oxygenation is already decreased.
You're off to a good start, but limitations like HOB filtration leaves little room for error on a new tank. Just slow down and let the tank do it's thing.



:)

You beat me to it... But yeah OP, don't kill the flow at night. I ramp my MP40s down just a bit at lights out but I still have a ton of flow going around the clock. Flow is so important for oxygen transfer in these smaller aquariums. It's amazing how fast even a couple fish can deplete oxygen in a tank with little flow... We're talking minutes.

 

[spencerkilgore]

Thank you everyone!! I read somewhere to cut flow so the fish can rest overnight. i’m gonna leave flow on permanently, also got a airbar. chilling with the dosing. @redseaenroute when you say everything i’ve been dosing like that i feel like an idiot… needed to hear that, thank you

@Mr. Mojo Rising just ordered the nitrite one! i have hanna for ammonia, nitrate, phos, and dKH (for the future, i dont test phos & dKH regularly)

 

[Troylee]

Sounds like a bacterial bloom and lack of oxygen… for fish only you don’t need to dose anything ever! just change water and the tank should be just fine. Nitrite is irrelevant and not worth testing and ammonia shouldn’t be tested after the cycle either as it shouldn’t be a issue.. also temps of 84 would take the oxygen levels down also try to keep it around 78 or so. P

 

[brandon429]

Its impactful science to you Spencer to know that reef tanks do not need, whatsoever, a connected filter. The entire surface area they present is bioload to your tank, your tank already contains the needed + extra surface area within the display.


Filters aren’t a benefit to a reef, they’re an oxygen tax, a co2 production tax, a waste acid tax etc. what the provide well is motion, and a power head supplies that without the assorted taxes.



And, to have one is a liability (the clouding within)


So knowing that helps you avoid this repeat.

To prevent this thread you would:

Disconnect and lift out the filter you don’t want. Take it out of the loop, that’s zero cloud.

Set in the filter you want, filled with all dry materials and no cycled materials (owing to the rule stated)

In a month of being in the water loop, your new filter is self cycled fully. At any time, you can instantly detach it for cleaning away from the tank. This is cloudless, so your crash won’t happen.


The reason any reef tank in existence can immediately detach a filter (if it’s done cloud free) and not crash is because of the rule above, it’s new cycling science.

Only the old science was taught to us, it’s why we were all initially trained to think extra filtration on a reef tank was not only helpful, but required and integrally linked. It’s not. It’s a huge liability that can be tolerated it you apply the right rule to the filter and if we handle that waste wrong, it causes fish kills. I have about twenty examples of this pattern, yours was #20 ish.

These are worthy studies because in the end new rules gained for cycle control end up saving fish.

 

[brandon429]

Here’s the one that directly preceded yours

Fish are struggling after water change

After doing my first canister filter clean and a 25% water change, my fish seem to be gasping for air and breathing rapidly. My test results don't seem out of ordinary. Anyone have any input? 29G tank. Fluvial 307 filter. 2 clowns, 2 fire fish, lawnmower blenny, sea hare, Valentini puffer...

www.reef2reef.com

Both threads are preventable by following the updated rules. New cycling science has a perfect safety record for a reason.

Filters are not commonly a cause of tank loss, I’ve ran them in the past too. They simply introduce variables (stores waste vs exports it) that clean-running designs will never see.

The danger is within the waste cloud. At no time was your ammonia off, or nitrite, the tests were merely tripped up by compounds other than ammonia and nitrite. An aerobic filter is not storing ammonia/hence it’s reason for use/ the kill agent in the waste clouding hasn’t been found… and I’m 100% sure old cycling scientists aren’t looking for it so it’ll be a while lol. They still believe your ammonia and nitrite were impacted.

 

[brandon429]

The big picture takeaway is that by knowing any extra filters are tolerated bioload, therefore taking them away or cleaning them deeply or not putting back with cycled material is all the same impact to your tank (zero impact) this gives you new cleaning boundary rules to change your reefing forever


The rule also applies exactly the same to the sandbed in your tank. It functions just like that filter does in terms of waste storage and liability, over time, relative to care variables as they present. New cycling science fixes your cycle control issues without ever testing for ammonia and nitrite again, you should throw out those kits. Your tank is cycled and can’t uncycle <— new cycling science.

To control a reef tanks safety during materials handling, simply store no clouding at all.

Always view reef tanks as having too much bacteria. What you are cleaning is a refresh, not a loss tax. Know that cloudless exposure in the water is what controls safety <— old cycling science teaches additions to fix issues: more bacteria, or more offsets added, new cycling science is about reducing the # of bacteria in a reef. Less (and diverse) is better, not more homogeneity.

There’s no time we need to test for ammonia or nitrite on a reef tank. I’m finding that to do so always causes reaction problems.


**I don’t see this thread as a mistake Spencer did, I see this thread as a mistake old cycling science teachers actively still cause.

 

[spencerkilgore]

The big picture takeaway is that by knowing any extra filters are tolerated bioload, therefore taking them away or cleaning them deeply or not putting back with cycled material is all the same impact to your tank (zero impact) this gives you new cleaning boundary rules to change your reefing forever


The rule also applies exactly the same to the sandbed in your tank. It functions just like that filter does in terms of waste storage and liability, over time, relative to care variables as they present. New cycling science fixes your cycle control issues without ever testing for ammonia and nitrite again, you should throw out those kits. Your tank is cycled and can’t uncycle <— new cycling science.

To control a reef tanks safety during materials handling, simply store no clouding at all.

Always view reef tanks as having too much bacteria. What you are cleaning is a refresh, not a loss tax. Know that cloudless exposure in the water is what controls safety <— old cycling science teaches additions to fix issues: more bacteria, or more offsets added, new cycling science is about reducing the # of bacteria in a reef. Less (and diverse) is better, not more homogeneity.

There’s no time we need to test for ammonia or nitrite on a reef tank. I’m finding that to do so always causes reaction problems.


**I don’t see this thread as a mistake Spencer did, I see this thread as a mistake old cycling science teachers actively still cause.

Brandon, the fact that you took a minute of your day to inform me without putting me down means so much to me. Thank you for this. I had no clue! This is very useful information.

 

[Lavey29]

I agree with the above posts but also wonder if 2 clowns in a 20g (15g with rock) created a stressful environment for the other fish then the tank changes contributed to his passing.

 

[Sleeping Giant]

Flow and copepods

 

[brandon429]

It’s very important to know if 25 reefers were sampled, 24 would disagree with the advice heh


we have a big nerd argument going on in the chem forum over this matter= was why the advice read like a deluge

my response is aimed to press back on what I feel is incorrect teaching models within the reef hobby.

What makes cycle debates / evolution in general / so slooooow is the scarcity of precision meters to tell us exactly what ammonia is doing, and by when, and how that varies in systems or if it varies much at all. All cycling debates reduce down to these basic unanswered questions and nobody really agrees on the seriousness or neutrality of the color shades we get with todays testers. The uncertainty will continue.

But I’m certain if no cloud happens, no materials handling losses will happen.

 

[brandon429]

One last big picture application of ‘the rule’ to overall lifespan of the system here. = testless materials handling to keep tank alive someday

One day it will be time to move or upgrade the system=materials handling challenge again.

So you’d lift out rocks and set them in a tote of matching clean water, temp and salinity only need to match. Rinse off the rocks with prepped saltwater sternly in the sink, so that adhered detritus doesn’t ride into holding containers (cloudless cleaning step one)

Then you’d set in the fish and corals and inverts into the containers, this is all cloudless transfer so nothing is going to crash

What’s left in the original tank? Sand, muddy water and messy tank walls. The rule says all that is tolerated waste plus bacteria, to be free of it at least occasionally is refreshing vs harmful…so all that mess get tossed we don’t need it.

We would for sure not seed one handful of sand into the new tank, there’s no deficit being addressed there’s an excess being addressed. We don’t have you people six ounces of old oil back into the bmw after an oil change just the same.

What’s running in the holding buckets is all the tank will ever need to control its cycle, the cleaned rocks, and this includes all future fish to be added

That means your rocks + current fish bioloading isn’t some matched balance where new fish added require time (or dosers for charge) to get bacteria up to par. That’s what old cycling science teaches

Your current rock surface area and current bacterial loading vastly exceeds the top fish bioloading you could run in that tank. This is why all filters are neutral in terms of helping with filtration (of ammonia)


There never was a deficit for them to address, because everyone’s rock is enough to cover all their future fish additions

Reef tanks don’t run low on surface area simply due to the type of rocks we use and where we place them. This means you are free to handle your sandbed without killing the system, or any connection the tank will ever see regarding filtration knowing the clouding is the thing we control, not a parameter from a test kit.

It means from now on when adding fish, or bioload to a reef tank, no extra bacteria consideration is needed

Or filters, or ramp up time or anything like that. You can use the certainty to make effective materials handling moves and never be at risk of loss, with no testing and no additives in play. That’s the benefit

The ruleset only applies to reef tanks not freshwater or qt setups or fish only setups

 

[DanP-SD]

There’s a lot of good advice on this post and, while I too believe it’s likely that either an oxygen drop or the excess additives were at play, keep in mind that the heartbreaking reality is that sometimes fish die without an acute problem in the tank.

If you don’t fully quarantine all livestock before adding it there’s always a risk the fish comes in with a pathogen that kills it. Sometimes transportation shock weakens them so something minor takes them out. Sometimes, they don’t eat or get bullied. Not trying to be depressing but, as you start up a new tank, some level of fish mortality is to be expected. You should be commended for your commitment to take on all the effort to save the fish and provide a good environment. I think the key take away from the advice above is that less is often more when it comes to our intervention in the reef ecosystems we create and that it’s important not to allow your passion for getting it right translate into overreacting.

I think the best approach is to figure out an overall strategy that provides the best quality environment you can and not overreacting to the bumps in the road. In my experience (30 or so years of keeping reefs; plenty of losses in the past; virtually zero mortality in my current tanks) the keys are establishing a solid reef ecosystem with high quality live rock, good circulation, reasonable filtration, rock solid stability in parameters), quarantining every creature you add (or buying quarantined from reliable vendors like Ocean Devotion who do the quarantining for you), and above all patience - stocking up slowly to let the ecosystem adjust to the bioload.

Consider this loss a bump in the road to building the tank you envision, keep posting your questions and taking the advice you’ll find willingly offered on this forum and make slow adjustments. You’ll get there.

 

[Lasse]

I think - like most of the responders in this thread - that its a combination of low input of oxygen (decreased mixing of bottom and surface water during night) combined with the adding of both microbacter products (that´s basically the same product as I understand and they probably also contain organic carbon) rising the oxygen consumption in the tank (the bacteria film you observe). The temperature of 84 degree F will also create a low contain of dissolved oxygen gas. At 35 psu 100 % saturation is only around 6,2 mg/L O2 at 84 degree F - calculator here.

The reason why you get the bacteria bloom after you switched out the TARARIUM aquarium filter is probably that the UV-C in it controlled the bacteria growth created of your addition of the microbacter products - when it was no longer in function you get the bacteria explosion. If you use products like the TARARIUM - a good trick is to use a plastic bag around it before you switch off the power and lift it up. In total opposition to some other experts in this thread - I think that filter like the the TARARIUM (without UV-C) is beneficial in a start up because it optimize the nitrification process. On the other hands - IMO - products like the two microbacter products that contain a mix of breakdown and nitrification bacteria is contra productive in a start up.

My advise would be to keep on the way you run it with the Tidal, stop all dosing of microbacter products - maybe run the TARARIUM with the UV-C activated (use floss to minimize particle) until the water clear up. Minimize your food during this time. Do not add any more "magical" additives of any sort - just do water changes and wait it out

Don't be mad at yourself - in my opinion this is a result when it works well but then you make a small change that has consequences that are difficult to see. In your case, your UV-C probably compensated for the increased growth of decomposition bacteria that your additions of microbacter products caused. This together with a little panic (using too hot water) poor circulation, less particle removal and addition of new chemicals probably caused areas with poor oxygen values and stress. Also add that cardinals can be a little tricky during the first months and - IMO - want properly oxygenated water - especially the Banggai cardinal.

Sincerely Lasse