My shrimps all love spinach...steamed or boiled. I use it as a treat.
So I lay my net in the tank and then put the spinach in it near to the back of the net.... 20 or 30 minutes and most will be in the net on the first try. Lift the net sharply at first then raise it out and dump your shrimp...
Dinner.... we catch those all summer.
Really not sure what species the OP is showing but it does look like our Atlantic Croakers.
If closely related, they do get rather large....we get them up to 16 and 22 inches.....and they they get larger than that.
I don't recommend an airstone in it.... more water is moved by bigger regular bubbles. Just the airline works the best. I even have extended the air line deeper into the filter and get a nice gentle current out of them. Adjust your air pump to move the most water with the least splashing or...
They can be used either way...air driven or mechanical.
If you are going to attach it to your mechanical filter, you should put it on the input side. Greatly increases your filtration. I have 2 attached to 2 small mechanical filters
They work very well driven by and airpump and can help...
I use our ceiling fan on high and a small fan or fans blowing across the top of the tank/tanks. Often it can lower the temps to mid to low 70's... approx 10 degrees.
You will need to have "top off" water available for the tanks daily.
#1 What kind of Pleco did you get...at times they might try to get the slime off of fish.
#2 You just got the tank?? Is it cycled? 3 goldies and a Pleco in a 20 gallon tank will be a ticking time bomb!! Goldfish get to big for 3 in a 20 gal. If they are small you will be ok for a while...
I agree that a bubbler will do about nothing in your filter....water is moving fast enough thru it.
All my tanks are low PH and they do/will take a long time to cycle. When I say cycle, I mean stable too.... be sure parameters don't change for a week or two minimum.
The longest time...