Thank you for reading....I wonder if anyone has any ideas what is wrong with my fish tank. The tank was set up 3 months ago with our two old bronze cory, aged 4 and 6 years. It was started with Fluval Cycle (daily, then weekly) and weekly 20% water changes, plants and ornaments (soaked for 1 week before adding).
Last week I added 5 young cory and all of them died, some were breathing heavily and stayed at the bottom, others behaved normally but suddenly started floating belly up and appeared weak. Within 3 days all perished. The 2 old corys appear to be just fine thankfully.
Since then I've done another 30% water change, increased oxygenation with an air pump and checked water parameters, here's all tank info:
Fluval Flex 57 with manufacturer's filter incl. Carbon pad, Temp: 24.5 C, 4W air pump /air stone Oxygen: 2-5 Ammonia+Nitrites: 0 Nitrates: 20-50 (fluctuating) Ph: 7 Chlorine: 0
I used to add Seacham flourish excel 1ml every other day but stopped since the young corys became unwell.
After another 20% water change to lower nitrates I've added 3 young cory and one of them has started breathing heavily on day two, another one has died overnight . I'm at a loss how to remedy the low oxygen and high-ish nitrates. Your advice is much appreciated!
Photo of the tank attached, all fish hiding under the ornament.
Sorry to read about this. Potential explanations are: * the addition of the 5 cories will have had a significant impact on the filter's bioload and capacity to process the fishes' waste, and these young cories weren't sufficiently robust to cope with this (following the likely stress of their journey to LFS, etc.) - did you check ammonia and nitrite levels during those 3 days?; * the water parameters (eg hardness/softness) are considerably different from those of where they came from / the LFS and this has caused a shock to the young cories; * something else not yet identified (and possibly the reason why the fish are hiding under the ornament).
A few more questions: * what brand and type(s) of test kit(s) are you using? * what is the ammonia and nitrate level from your tapwater? * what dechlorinator are you using? * just a thought based on someone else's experience I read recently - is there any algae-like substance under any of the ornaments or evident anywhere such as on the corners/joins of the tank?
Thank you so much for the reply! So, it does sound to you like it's stress related in conjunction with some water parameters? Unfortunately I only got tests once the problem had occurred and used tetra dipsticks for ammonia and for pH etc, then a liquid tetra test for oxygen and a liquid nutrifin test for nitrate....the api master testkit will arrive only tomorrow so potentially the dipsticks didn't give an accurate result for ammonia and nitrites? (both tap water and tank were 0, and tap water nitrites 0, nitrates minimal) My dechlorinator is Tetra too, the blue stuff with anti stress ingredients. Regarding the algae, would you be able to point me to that thread? There's only one type of algae in the tank, a little on the ornaments and on the side, see photo, it's like very thin brown patches that I rub off weekly. Thank you once again for your input!
I'll have to be brief (apologies) but can now eliminate the following as potential possibilities: * algae - I'd read on another forum about cyanobacteria (blue/green algae - very different from yours) having a fatal effect, but your algae is fine; * lack of ammonia in the tapwater = good - I had wondered whether you might have chloraminated water and may therefore require a water conditioner or dosage that specifically addresses that rather than just chlorine, but yours doesn't seem to be chloraminated (unless API Masterkit suggests ammonia in tapwater).
Final question: * what is your water hardness in CaCO3/ppm or German degrees hardness? [If in UK, input postcode into water supplier website to find out.]
Just a quick addition to say both ammonia and nitrites are zero with the API master kit... Nitrates are ca 30. It's still puzzling to me why nitrates are so high, and why the young cory have now all died...
Apologies in advance for brevity: * cories do well with soft water, so your German degrees hardness levels are great and oughtn't to be any problem (unless, for some reason, the LFS has hard water and the contrast was a shock to them); * daily water changes of 10% might be a plan for now, and help dilute any stress hormones that may be around; * what are tap water nitrate levels, with API Masterkit?
API master kit says Nitrate of tap water is zero, tank Nitrate has come down a little to just above 20.
Does the flow rate impact at all how well the biological filter deals with nitrates? I had set the pump to the highest flow rate (600l/hr) to generate more oxygen. Having looked online at Ex-Nitrate by Seachem, it says the flow rate should be no more than 200l/hr for this product to work. Is this the reasoning behind it?
It may well do but, more importantly, the high flow rate could well be the cause of the cories hiding under the ornament. I've found some species of fish particularly affected by flow rate, some fatally (inability to cope with it on entry into tank seemed to result in them struggling/'drowning' within minutes) and some stressed and hiding in quieter parts of the tank, while others struggled as they became older and weaker. It might be that your young fish are struggling, while the older ones are more robust and have got used to it. I would definitely lower the flow rate for now and see if that helps at all - both in terms of the fish and the nitrates level.