Fish dying

[DonC]

Hey guys so I have a well established 75 well planted with about 65 nano fish 8 dwarf crayfish and about a dozen nerite snails with great all around water parameters. I used to be around the 20 to 40 ppm nitrates but in the last 6 weeks its been around 5 to 10 ppm maybe because I added more plants back then and my original plants have really popped not quite sure anyway I have been doing a 35% weekly water change and in the last 25 days I have lost 4 fish 2 dwarf crayfish and 2 snails. I was wondering if my nitrates have been that low maybe the 35 % water change could be the problem. I’m thinking to cut back to 10 % weekly or 25% every 2 weeks or should I just monitor the nitrates and when they get a bit high do the change.
What do you think?

 

[Essjay]

Nitrate should not be used as a guide to when to do water changes, they should be done weekly regardless of nitrate. Plants take up ammonia leaving little for bacteria to convert to nitrate. But the other things which build up in the water, things we can't measure, still build up even if plants keep nitrate low. And things in tap water get used up, which are replenished by regular water changes. Many of us change at least 50% every week.

How often and how much were the water changes before you added the extra plants 6 weeks ago?
Water changes, if done regularly, don't usually harm fish or inverts. It's when water changes are small and infrequent, then a larger change is done that problems can happen. This is because small infrequent water changes allow the tank water chemistry to drift away from tap water chemistry, then when a bigger change is done, the tank water chemistry changes a lot and this shocks the fish.