Lost two corycats... cause?

Beckett

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Hi there, I have had a school of 7 bronze corys in a 38 gallon tank for about a month and a half now. They are in with 7 peppered cory cats and I just added a school of 12 diamond tetra last night. Unfortunately two of my bronze corys have died and I am not sure why. I am hoping folks on here might have suggestions for me so I can avoid anything else happening.

My tank is planted and fully cycled. I did a fishless cycle over a span of 3.5 weeks with API starter bacteria added in. I tested water parameters throughout that to be sure the tank was cycled. I keep the tank at 76 degrees F. The bronze corys have never shown signs of stress. They are very active and have actually been spawning regularly in the tank. Yet somehow I am down to 5 now.

I thought one that I found between some river rocks maybe got itself stuck there and couldn’t get out. So i filled that space in some with gravel and sand substrate from another area in the tank to try and block the crevices better. Yet i lost another cory two days ago.

Now I am wondering if I could be under feeding? I try to feed light to avoid making a mess and screwing up my water parameters but maybe it’s too little? For the original 14 corys I fed 3 hikari bottom feeder wafers in morning and at night, so 6 total each day. Is this too little? There is also a juvenile BN pleco that picks at those wafers too.

Also I tested my water again today and yesterday before a water change and everything looked good. Nitrates at 20 ppm before my water change, no ammonia or nitrites detected.

Also the second to die was a large breeding female I had watched lay eggs in the past couple weeks.

Any tips would be greatly appreciated!
 
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Beckett

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Oh and the second one died BEFORE the Diamonds were added, so it couldn’t be something from them or store water.
 
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Beckett

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Ah, I worded that poorly. I did not transfer any store water into the tank. I put the fish into a separate container and slowly added tank water to it. Then netted them and placed them in my main tank, so the only water would have been the few drops on each fish maybe.

I did go out and buy the API Master Test Kit, I had been using the plastic test strips up until now. The test kit did vary some from what the test strips had been telling my. My PH is much higher than I thought, the strips read 6.0 but the API kit says 6.8. I checked and that PH should still be okay for the species I have in my tank (Diamond Tetra, BN pleco, Bronze corys, Pepper corys).

My ammonia and nitrites were both at zero which is good. However my nitrates were up at 30 PPM and I just did a 25% water change on Friday. This was a bit alarming to me and I now suspect the nitrates have been higher than the test strips have been showing all along. I have never gotten a test higher than 20PPM on the strips, even at the end of the week when I do my water changes. Could that be the cause of my bronze corys dying? They never showed signs of stress prior to losing them.

I did a 50% water change last night and am going to retest my water today. Really hoping I got the nitrates down, and I am ordering a live floating plant today so hopefully by the end of the week that will be in the tank too, to help consume things directly from the water.

Also, when should a water change happen? When nitrates are at 10, 15, 20 PPM?
 

essjay

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First test your tap water for nitrate. That is the lowest you can get it by water changes. If that is below 20 ppm, you should aim to keep the tank nitrate under 20.
Water changes should be 50%+ a week regardless of the nitrate level. I have less than 5 ppm in my tap water and my tank also reads less than 5, but I still do water changes every week.

Nitrate is not a fast killer, so a level of 30 ppm wouldn't kill the cories quickly. But if your tap nitrate is a lot lower than your tank it does suggest you need to increase your tank maintenance. Do weekly water changes of at least 50%. Clean the substrate regularly; if you have gravel deep clean that. Wash your filter media at least once a month in old tank water - every 2 weeks is better.


When you tested nitrate, did you shake bottle #2 and the tube like the instructions say? That shaking is important. Most of us shake the bottle for longer than they say to. If the bottle and tube are not shaken the reading won't be accurate.
 

seangee

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It would be informative to test the nitrates in your tap water.
Personally I change 75% of the water once a week regardless of readings and recommend 50% as a minimum - nitrates are not the only reason for water changes.
I feed my 30 cories 2 or 3 wafers once a day on the days I feed wafers so you are definitely not underfeeding. They are primarily carnivores so I do tend to mix up the foods and they only get wafers once a week. Fluval bug bites are a favourite and so are Omega One shrimp pellets.

None of these things are likely to have killed your fish though ...
 
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Beckett

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Thanks for the replies! I did shake the tube, a bit longer than recommended too. So hopefully my reading was accurate.

I will definitely test my plain tap water tonight after work, I had no idea there could be nitrates in the regular tap! I will also retest the tank water to see how things are faring after the 50% change last night. I also rinsed my filter media in tank water last night as that was just about due, probably was 3.5 weeks ago I last cleaned it.

My floating water sprite is also on the way, so hopefully that will help me out a little.

For diet I have been feeding Hikari Wafers mainly, Shrimp pellets a couple times a week, Fluval bug bite sticks maybe once a week. I could probably increase the shrimp/bug bites and reduce wafers just to try and be more balanced for them.

I'll post again after I do my testing tonight after work and will plan to up water changes to 50% going forward. I am wondering if my nitrates have been high this entire time I've had my fish (2 months) and I had no idea because the test strips were not accurate.

Also sounds like I could reduce my feeding, I only have 12 corys so maybe 1 wafer in morning and 1 shrimp pellet at night or something?

Edit--- I do vaccum my gravel best I can each water change, so once a week. I have live plants so it's a bit tough to get super close to them without sucking up roots or root tabs I placed in the substrate. And I have some driftwood I don't move, but I do my best to hold the siphon around the base of it and my larger river rocks to get some of the waste out. Do I need to pull up driftwood and larger rocks each cleaning?
 
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essjay

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No, just hoover round the decor and plant roots.

Some areas do have high nitrate in tap water, mainly agricultural areas where a lot of fertiliser is used.
 
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