Zebrafish Bacterial Bloom turning water pink/reddish?

[KSA]

Hello fellow aquarium enthusiasts

A week ago I set up some new Zebrafish tanks with 15 zebrafish pr. tank. Before adding the zebrafish to the new tanks and water I added TetraSafe Start bacteria to the tanks. The tank water is made from RO water with InstantOcean (60mg/L).

The pH has been stable in the range of 7.6 - 8.4 and the Amonia, Nitrite and Nitrate levels have stayed near zero.
As expected, there have been a large bacterial bloom. However, the water have started to turn a pinkish/ reddish color (see image links), which I do not understand. my only explanation could be the feed color, but the fish are feed very very sparsely.

Any advice is highly appriciated

image links:
https://postimg.cc/75rCKrZh
https://postimg.cc/30M7376D
https://postimg.cc/pyqb0fVF

Best Regards
Kristian Andersen

[rlederer]

Well it seems to me that the tanks are not cycled and you have a bacterial bloom. Tetrasafe is not going to act that fast. The pink color could be from the food or algae in the tank. And I don't understand why you are using Instant Ocean. Isn't that for seawater?

[KSA]

Thanks for the reply.

How would you handle the bacterial bloom in the tank? There is no filter. Instant Ocean is used worldwide in zebrafish facilities, to add salts back into RO water. However, I'm starting to question why, as it mostly is composed of NaCl... but it is what is done everywhere...

How do I figure out if it can be algae?

[rlederer]

I didn't know that Instant Ocean was used in freshwater. New to me. There is a product called SeaChem Replenish that is specifically made to temper R/O water. I've used that with success. I'd do a water change every day, say 25% to treat the bacterial bloom. I don't know how to determine if the pink color is algae except to look at a water sample under a microscope.

If you have no filter, where would the bacterial colonies grow? In the gravel?

[Aiken Drum]

I dont want to criticize or anything, but im curious as to why you have gone down the route you have.

- Im presuming by Zebrafish you are meaning Zebra danios?
- Why are you using remineralised RO water?
- Why dont you have a filter?

[KSA]

It's a quite low concentration and it's what is used in all the zebrafish research facilities, that I know of. But maybe it is something to reconsider. Will the bacterial bloom be able to fade with that large regular water changes?

They are Danio rerios.
We remineralise the water to provide some minerals/ salts in the water for the fish.
We dont have filters because it is a temporal solution, so we just normally do regular water changes.

[Aiken Drum]

Is keeping Zebra danios in this manner something you have a lot of experience in?

I see youtube videos with unfiltered tanks, but its not something i personally know anything about. Bacteria blooms are usually caused by excess nutrients caused by an uncycled aquarium. Not having a filter must make cycling the tank much, much harder.

I understand what the purpose of remineralising RO water, what i dont get is why RO in the first place. I, like 99% of aquarium keepers with zebra danios use dechlorinated tap water. Zebra danios are very hardy, and i wouldn't consider RO water without reason.

[rlederer]

The bacterial bloom is supported either by organic matter in the tank or organic matter in the water itself. If you are using R/O water, the water quality should not be an issue, so if you keep replacing the water you should be able to lower the level of organics in the water. But it also depends on the size of the tanks. If you have 15 fish in a 10 gallon tank, the organics are going to build up quickly via food and waste.

[KSA]

We would like to have very controlled water parameters for research purposes. Therefore, we use RO water. Obviously it's not going very great with the bacterial bloom.

[Aiken Drum]

Ah. I see. You are a scientist breeding zebra danios for research? I'm intrigued now. Ive found an article on this, so ive found my bedtime reading. Sorry for hijacking your thread with questions rather than answers.

[KSA]

No worries Aiken.
All insights and questions are highly appreciated!

[KSA]

Since posting I have lowered the amount of fish in each tank. I have not done daily water changes, as many videos on youtube and internet article say to leave the water to clear. I'm used to working with big zebrafish systems such as (https://www.tecniplast.it/us/product...echnology.html). I'm not used to having the fish in these seperate tanks.

[KSA]

Rlederer

Since posting I have already tried to lower the number of zebrafish in each tank. I have not performed daily water changes, as many internet sites says not to do so, and leave it to clear by itself. But I agree with you, it would be good to get rid of all the bio-waste.

[Autumnsky]

Also since you have no substrate or filter why not remove the fish from the water to a new water holding container.

Clean the containers. Make sure to clean as to kill bacteria in the bacterial bloom. Super thoroughly rinse the containers.

New water and then start over.

disclaimer: No experience here with scientific experiment or why it needs to be done.

Adding the correct type of remineralizer for fish to more closely replicate natural water would be more beneficial for the fish, and they would be healthier.

Keeping fish in unsafe water parameters will make experimenting probably not accurate because fish will die from unsafe ammonia, nitrite and nitrate, ruining your experiment I would think.

The amount of food you are feeding is likely the problem as well. Reduce the amount of food added and how fast you add it. Just to the amount they can eat in a minute. Add some food let them finish eating it all then add a little more to they quantity of what an estimate of a normal feeding would be.

Then in relation to the salt added in the water this info popped up, might mean more for you.
https://www.nature.com/articles/srep18597

The remineralizer additive has a good combination of ingredients necessary for osmoregulation.

Also the color of the food certainly could tint the water pink.

What are the ingredients of the food?