I ised a 2 inch gate only out of inexperience lol. See i figured both 1.5 inch siphons would need the larger gate but after seeing how little the gate is opened i feel like you woulf be fine with the 1.5 inch gate. I want
ragin_cajun
to chime in before you make any decisions based off my advice. I'd rather be proven wrong than give you bad advice
Meh all these heaters fail eventually find one that lasts let me know lol
If you're using a pair of 1.5 inch drains, I THINK you'd be fine with a 1.5 inch gate. I have 2 inch siphon drains, I used a 4 inch slice gate, and that is just WAY too big. Frank started doing his tank, we talked back and forth a lot about this. As you can see, he went with considerably smaller gate than 3 inches for 2 1.5 inch drains, and he's saying he could well have used a smaller gate vale.
If you went with a pair of 1.5 inch drains, AND you're SURE you won't want to upgrade to 2 inch drains later, you should follow Frank's advice and go with 1.5 inch slice gate.
Now, about 2 inch drains. I have a 540 gallon tank, I ran 2 inch siphon drains thinking I might one day go with even bigger pumps than the pair of 2400 GPH Laguna's I have now. I never needed bigger pumps yet (fish only, freshwater). I could have gone with 1.5 inch drains to be honest.
So could you in a 330 gallon tank. If you decide to go saltwater one day, you'd probably still be OK with 1.5 inch siphon drains since the higher circulation required for nice reef tanks require either power heads or closed loop from the floor of the tank to get directional control of increased flow on corals.
1.5 inch drains, 1.5 inch slice gate, gotta be all you'll ever need in that tank. At least with fish.
I don't keep stingrays, if you want to you should post in their section and ask them what flow rates you'd need. I really think if I had rays, my flow rates would be fine (6-8 times turnover in a 540), but I'm just guessing about that.
Don't forget to plan for a drip system. The drip and filter socks are the greatest thing I've ever done. Put a controller on your heaters, too. On all your tanks. All heaters freak out eventually, and you'll be keeping these fish for years. Think in terms of years on all this equipment and tank plans.