Tank issues- Substrate?

[MaryBeth]

Hi,

I have a 10 gallon planted tank. In this tank I have guppies and Cory doras.

I have a couple issues in this tank. The main issue being that lately I’ve had some of my guppies dying, and I’m not entirely sure why. When I test the water, everything always comes out fine.

I’ve had an issue for awhile now where the filter seems to get clogged up. I generally can take out the sponge and clean it and it’s fine. But it’s a lot of dark gunk in there. I was wondering if anyone has has this issue with their substrate or any ideas on what I can do about it? Or if it’s a different issue than this?

I have also always had some pest/pond/whatever snails in there, but I got assassin snails awhile ago that seem to at least keep the population at a fairly reasonable level.

Thank you so much for any help!

 

[SaraB]

What substrate are you using? The corydoras may be stirring it up sending it into the filter. You could use a sponge prefilter for your intake, it will prevent the substrate from getting in the actual filter.
How many fish are in your tank? What is your water change schedule like? How are your guppies acting before they die? It could be a disease running through your tank.