Should my filter intake be high or low?

My preference is to have the intake placed as low in the tank as possible. This allows for better water circulation(since there are many components in aquarium water that are heavier than the water itself so they are more concentrated on the bottom) Which is important especially for your bottom feeders as they hardly ever come up from that level of the water and can often be the first ones to suffer if there is any high concentrations of ammonia.

The intake should be as low as you can get it in the tank. The toxic products of the nitrogen cycle (ammonia, nitrite and nitrate) mix with water throughout the tank, but are concentrated at higher levels toward the bottom of the tank.

Drawing from the lower area of the tank will keep these chemicals mixed at a lower concentration throughout the tank as the water is taken from the bottom and returned at the top.

Then, when you do your weekly 30% water changes, you will be removing the toxins at a higher % no matter where you siphon from.

If you can't get the intake tube really low, then always siphon from the bottom quarter of the tank to remove the highest concentration of toxins. Do a gravel siphon once a month too.

You don't need to have to filters, although it does not hurt to have two.

You should place the intake lower to the gravel. Because various debris, waste, uneaten food etc is heavier than water, it will sink. Having the filter intake nearer the top will make for less effective filtration because the water near the top is cleaner to begin with.

It also makes for better water movement, because the water is taken from the bottom and dumped back into the top, creating a water cycle that covers most areas of the tank. If the water is take nfrom the top and dumped back into the top, the water near the bottom will have much less water movement.

If you want to keep your intake up high, you could put a small power head (water pump) near the bottom to circulate the water, but that might defeat the purpose of trying not to waste room for your bottom feeders.

Anyway, it should be okay if you leave the intake up higher, as long as you do weekly water changes and gravel vacs.

A higher intake may suck up less waste from the bottom, but it won't harm the tank to have it higher.

Low. If you watch things like food particles, they spiral around and eventually go down. Having in and out where they are makes this possible. I once got Tetra to send an extension free for the Whisper 30, because I was using it in a 25, which is rather deep and it was only about half way down.

In a tank that big it is always better to have 2 filters, that way one intake can be low and the other high. Since you only have 1 having it lower would be better so it catches more debris before it falls and gets caught in the gravel.

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Given the choice I would place it low. This picks up more waste from the bottom and also encourages better "turn over" of water in the tank.

MM