D&RW, I think what folks here are trying to tell you is that if you would have mentioned some of this stuff to us, we may have been able to counsel you BEFORE you made the purchase.
For example, I would have told you to run (not walk) from a Little Giant pump. They are notorious for failing and not very long lasting. You can definitely google the myriad of bad reviews on that.
Based on your size pond, the single aqua art retro bottom drain would have been perfectly suitable for you. It does say very clearly on the site that the large AA drain is good for up to 10,000 gallons.
That oxygen testing thingee---we would have totally told you not to have wasted your cash.
We really, really, really want to help you. But to do that, you've got to clue us into your plans so we can help guide you BEFORE you spend the dough. We might have been able to have saved you those restocking fees.
And, of course, if you want to just go ahead and make the purchases, you are more than free to--after all, it is YOUR money. But you can't ask us to then ban a web pond retail shop after the fact, because they don't want to return the stuff we likely would have advised you not to buy from the beginning had we heard about it.
I don't want to see anyone lose money, and I am certainly not a fan of restocking fees. So, I do my hardest to do all my due diligence up front.
D&RW, I really want you to be successful at this ponding hobby and love it. I confess I am not fully clear on what your overall plan is for your filtration, etc. You've not clued us in on the full plan--we just hear about the single things you buy (or return) here and there. How can we help you now so that you don't have to return anything later, but get a good system together up front? We are here to assist you. Do you have a full sketch of your pond and it's systems that we can see?
Please don't think for a minute that we're somehow lambasting you. We will all never agree on everything, and will certainly tussle a bit on our opinions. When there is more than one way to filet a fish, it's par for the course.