Fish getting stuck to the filter

Question
Hi! I have two clown loaches, 1 bala shark, and 1 platy (The other one died). I have a 12 gallon tank with the filter and light built into the top or cover of the tank. I noticed the tank was cloudy and my platy was dead. Then I saw my two clown loaches stuck to the filter. I thought they were both dead so I lightly shook the tube and the two clown loaches came off and started swimming around. They were alive!!!! The filter tube comes down almost to the bottom of the tank and has a square box at the end with holes for the water to run through. Why are my loaches getting stuck to the box with holes? How can I fix this.  

Answer
Hello Alyssa
It seems like you have some sort of chemical imbalance in your tank. It takes a fair bit to kill a platy as they are pretty hardy fish.
I would take your water in for testing to your local fish store - it could be high ammonia and / or nitrites which would make the fish slow (nitrites can cause a fish to suffocate) - at which point the filter is sucking them onto the intake.
The reason I suspect this is that you've mentioned milky water - this is usually common in newer tanks that are still cycling (establishing the right bacteria to convert ammonia to nitrites to nitrates) at which time the fist two of those three spike to pretty high levels and result in fish losses. How long have you had your tank up and running? A water-test at the LFS will tell you if it is the result of cycling or if you're just over-stocked.
The first thing to do is several water-changes on a near daily basis (25% daily for 4 to 5  days) - if your tank is cycling, this will make it a little easier on the fish too - and draw out the pollutants from the water but turning over your entire tank volume.
The other long-term problem you have is over-stocking - a bala-shark is too large for a 12g tank - they get to be nearly 14" with the vast majority of them growing to over 8" - and they love the room to swim around - making them more suited to something like a 55g. It's the same with your loaches - with an adult size of 8 to 12" (sometimes more). It may be a good idea to see if you can trade for more suitable fish.
Given that your filter is part of the tank, it's not going to be over-rated (for a higher volume / flow rate) than what you need, so it's very unlikely that it si the direct cause of problems. all your fish are farily hardy and unless sick / stunned wouldn't be drawn into a filter.
Good Luck
Shawn