Hi and welcome to the forum
What is the GH (general hardness) and pH of your water supply. This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
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Have you tried putting your blue rams together instead of having 1 in each tank?
If they get along you would have more space in the smaller tank for the guppies and platies. You could then set up the small tank with hard water for livebearers, and have tetras, angels and other soft water fishes in the bigger tank.
You should get 3 more Julii catfish so you have a group of 6. They prefer to be in groups.
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You can get round/ cylindrical sponges for some types of internal power filter. These cylindrical sponges have a hole through the centre of them and usually fit over the intake strainer of external power filter and provide additional filtration as well as helping stop small fish and shrimp being sucked into the filter.