https://www.vetsurgeon.org/f/clinical-questions/9027/help-with-tropical-fish-please We have a large sized (delta 300) tropical fish tank that in the last 24hours we have lost several fish. They are mainly the smaller fish, danio&#39;s, tetra&#39;s and botia&#39;s etc but some of the larger ones are quite old now and are worried we are going toen-USTelligent Community 10https://www.vetsurgeon.org/thread/43265?ContentTypeID=1Tue, 16 Aug 2011 07:36:23 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:f700e013-7bba-4b0e-9588-63e9ec6779a9Mark Hedberg<p>Fin rot is usually secondary - fish that have had immune system depressed can develop it. Totally agree on the water changes, but carefully.</p> <p>Very often tank fish can suffer from chronic low grade stress from imperfect water quality. How much water do you change in these monthly water changes? Do you use tap water? If yes, be warned that tap water can contain high levels of chlorine, which is irritant to fish. Yes, after a while the chlorine evaporates out, but these periodic water changes can actually increase the stress on the fish temporarily. </p> <p>Plant life - do you have lots of plants in the tank? This can affect the levels of dissolved oxygen in water.</p> <p>&nbsp;</p> <p>&nbsp;</p><div style="clear:both;"></div>https://www.vetsurgeon.org/thread/43098?ContentTypeID=1Thu, 11 Aug 2011 20:51:37 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:4c3b6e4a-2763-4840-9c40-aaa560dcd03dGillian Mostyn<p>I&#39;d agree - get the water checked ASAP.&nbsp; </p> <p>If that is OK, then maybe ring one of the path labs that deals with exotics and ask about getting some pathology done on any further fish that die.&nbsp; Sometimes if you are losing a lot of fish it is the cheapest way to get an answer.&nbsp; Unfortunately fish tissues go mushy pretty quickly so sometimes sacrificing a sick fish to get a better sample is a good idea. </p> <p>Hope things improve. <img src="https://www.vetsurgeon.org/emoticons/v2/Fingerscrossed.png" alt="Fingers crossed" /></p><div style="clear:both;"></div>https://www.vetsurgeon.org/thread/43062?ContentTypeID=1Thu, 11 Aug 2011 15:47:36 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:240c06b2-a13a-4e1a-9b70-583de679e4c0Edward Jones<p>Check the basic water parameters: ammonia, nitrite and nitrate. Usually your local aquarium shop will be able to test it for you to save forking out for a test kit.</p> <p>If either ammonia or nitrite are not zero then do a few partial water changes to bring it down and feed much less in the mean time. Nitrates are less important - it&#39;s probably crept up but when this happens gradually the fish usually adapt okay and some water supplies are rather high in nitrates anyway.</p> <p>How much water do you change on a monthly basis? You might be better doing 10% on a weekly basis. If the ammonia and nitrites are high then water changes are the only way of getting them down again, but sudden big water changes might be too much of a shock.</p> <p>There are other possibilities of course (e.g. infectious disease) but you need to rule out a problem with the biological filtration first.</p><div style="clear:both;"></div>