To be honest, it sounds like way too many fish for that size aquarium, at least at first until the filter and the aquarium has cycled itself (nitrogen cycle.)

I currently have 3 small fantails and two 7 inch koi in 120 gallons of water, and even then the nitrite levels are currently spiking. I've been doing 30% water changes for the last few days. The ammonia level isn't too bad, however, so I am hopeful that has levelled off.

I assume you have an adequate filter, but goldfish/koi are known for lots of waste (due to their big size) so a bigger filter than you normally would use might help. Else, perhaps water changes until things stabilize.

You really should be testing for ammonia and nitrite if you haven't already done so. You may find the levels are getting pretty high. Cloudy water is idicative that somethings not right, or you are feeding too much and excessive waste. If so, water changes are one way to try to keep ammonia, nitrite, etc manageable.

I have an undergravel filter and a filter on the back ( biological I beleive) I will get a test kit and do a water change this weekend

I recomend the 'Master Freshwater Test Kit' by Aquarium Pharmaceuticals. It is very acurate and inexpensive. I wouldn't wait until the weekend to PWC. You should test 0.0 ppm ammonia and 0.0 ppm nitrite, any thing more than 0 with ammonia and nitrite is toxic. If nitrite is high , salt can be used to block nitrite poisoning to a degree. Nitrate should be