[Whats best/appropriate for cleaning these hang ons?]

I have the Penn-Plax- Cascade 300, and a Top Fin PF75, hang on back filters for a 75 gal freshwater w only 1 fish.
1 Full grown comet goldfish thats 10 inches long. Since my kind of goldfish is large and produces more waste,
how often do i clean them? How do you recommend cleaning them? want to survey to see whats most common and also new ideas that i might've not thought of.
Also is it just recommended to clean by rising in old tank water or de-chlorinated water?
Are you supposed to replace cartridges every 2 weeks with brand new ones also? or do u think it loses bacteria too quick?

[Looking for python and pump combo plz help asap]

Would anybody be able to help me with a link to buy a python system and the electric pump needed to pull out water of the aquarium? I really need one about 75ft for my 75 gal freshwater thats outta cycle. Ammonia 1.0, nitrite 0, nitrate 20ppm, ph 8.0 cuz of well water. Please share wheres the cheapest youve seen these water changers so i may buy one asap. I need a hose for 50ft 

[Goldfish food? How to know Plz help asap]

How do i know what goldfish food is safe for all goldfish and ones that are safe for only certain varieties of goldfish?

i get confused w the saki hikari ones where it says for premium-grade types of goldfish, fancy, and ranchu.. why doesn’t it say safe for all goldfish?

[Easy green all in one fertilizer by aq coop question]

Is the easy green all in one fertilizer safe for all fish is it meaning? Is it specifically safe for goldfish ? Plz help asap. I have one large hornwort plant w dark green instead of light green leaves. Theyre only light shiny green on the tops and one anubias frazeri. Will be adding 1 java fern soon also. I have a 75 gal w only 1 full grown 10” goldfish.