Help - What's Next?

Hi all, I'd love some advice from you knowledgeable folks. Most of my fish are flashing.
The details and parameters of the tank are:

Species: Guppys & Panda Corys
Tank: 180 liter - cycled and running for 3 months
Internals: Bare-bottomed (ceramic tiles), large Mopani driftwood (still leaching a lot), lots of epiphyte plants
Water: Council water + Prime de-chlorinator + crushed coral (I'm in CT)
Water changes: 33% weekly
pH:6.9
KH: 5-6
GH: 4-5
Temp: 24,5c
Nitrites, nitrates, amonia: negligible

I have already run 3 weeks at full strength of Seachem Paragaurd - but there is no difference in the flashing behavior. There are no other apparent symptoms or signs other than the flashing.

I would love any and all suggestions on what I should be doing next. Thanks.

 

In terms of frequency - if you sit and watch the tank, within 2 minutes you will see a fish flash. Both Gupps and Corys.
Started as soon as I got the first fish. The tank has been up and running for about 3 months - so effectively all the fish are new.
Each batch was quarantined for 2-3 weeks with Paragaurd as a prophylactic for parasites.
The main tank is 2 weeks into another 3 week treatment of Paragaurd.
Flukes are meant to be one of the ectoparasites covered by Paragaurd.

I can say that the one strange thing that I cannot explain is that besides the large piece of Mopani still staining the water with tannin - it also makes the water cloudy. Like a cup of tea with a couple of drops of milk in it.
The result is that my water is NEVER crystal - and progressively gets more brown + cloudy towards water change day.
I have read that if you have a lot of silt (from substrate) in the water - it can make fish flash. I have a bare-bottom tank - so I wonder first, is this milkiness coming from the Mopani, and second, is it maybe the ongoing cause of all the flashing?

 

I have lost a few Corys over time, but I assume that's the sensitivity to the Paragaurd.

 

Yea - I don't mind the tannin. The milkiness however I really wish would go away.

 

Everything seems fine.... I would suggest trying either bigger waterchanges or more often and see if you don't see a change in the fish behavior, the milkieness is not really good.
Also maybe take a sample of tank and municipal water to your LFS.. just to double check your test kit... you never know
I would remove the ceramic tiles also, you never know what could have been used in the manufacturing process (or what could get trapped under it), add some pool filter sand as that also provides more surface area for beneficial bacteria to grow on and cories love digging in substrate
What kind of filter are you using?

 

My two cents ;

What exact are the levels of ammonia, nitrites and nitrates?
I think it is quite odd nitrates are still low though there are no heavy feeders amongst the plants.
Is the water treated for chloramines and such?
How often is the filter cleaned?
Is the Ph stabil as far as you know? Your water seems quite soft which could cause Ph swings (adding Mopane).

Of topic : Corys don't do very well in bare bottoms.

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Thanks for your input @GaryG - I'm running an Aquael ULTRAMAX 1500 Canister Filter, rated at 1500 liters (probably half of that real-world). It has about 2kg of Matrix in it.
I pre-filter before the canister intake even - coarse sponge, fine sponge and then filter floss.

 

Thanks for your response @DoubleDutch
I'm sure nitrates are very low because the tank is still under-stocked. 180 liters with 10 male guppys and 3 pandas - lots of plants + 33% w/c per week.
Yes I treat the replacement water with Seachem Prime every week before refilling the tank.
I open the canister once a month. I also have a pre-filter system before the canister intake even - coarse sponge, fine sponge and then filter floss. This is maintained weekly.
Every time I take water tests, the readings are pretty much the same - so I am unaware of any swings.
I have 1,5 cups of crushed coral in a media bag, inside the canister.

 

Thanks @A new day
I can try feeding less. My feeling is that this is not the issue however. I've kept aquariums on and off my whole life, and as you know, you get a feel for too much and too little.
Usually, too much food comes with algae blooms. My algae situation is one thing that is good - haven't had a single spot in 3 months yet. (He says holding thumbs)

 

Questions aswered !!! Good thinking about everything. How did you cycle btw ??

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I started fishless - fed the tank a pinch of food for two weeks. Then I introduced the first 5 guppies and made sure I didn't overfeed while the cycle/tank matured.

 

@A new day @GaryG @DoubleDutch
Just had a thought - as stated above, the tank is currently under-stocked - Juwel Rio 180: 10 male Guppies + 3 Panda Corys
Do you think it's possible that the perpetual cloudiness is being caused because there are not enough fish to keep a colony of beneficial bacteria fed?

 

Given this some thoughts. I think it is the understocking causing it in combination with the cycling.

Bacterial Bloom are heterotropic bacteria feeding on all kind of compounds temporarily available in mostly new set ups. Normally plants and these bacteria use these compounds till there is a kind of balance. Then bacterial bloom will go on its own.

This tank seems to be in an unbalance and
my suspecions / thoughts go to the "small cycling" in a huge tank / filter which is quite / too understocked to keep the cycle running and population of the filterbacteria fed / grow. The plants aren't big "eaters" as well.

Not meand offensive or whatsever but what I mean it looks as if this huge tank (for our standards it is) is cycled and stocked like a fishbowl.



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@DoubleDutch thanks for this - I think the puzzle pieces are starting to come together.
I presume that I should be increasing aeration during and until the problem is resolved? I think I once read that bacteria blooms use up a lot of oxygen in the system?
Another question - do you think (if it is a bloom) - that this could be the cause of the flashing behavior?