IMHO a skimmer should be your next purchase. I was unconvinced of the need for one until we got one. All it took was looking (and smelling) the skimmate and I knew that this was stuff I did not want in my system.
In fact I recently had to turn mine off for a week due to some additives my husband added to the system and I was freaking out. It is back on now trying hard to pull the mess out of the tank. I am afraid to test my water since things were going so well before and I know it will depress me.
Without one waterchanges are even more critical as is all other tank maintenance (cleaning sponges etc). Stay on top of it and things will get better. Hopefully before anything truly bad happens.
Best of luck and let us know if we can be of more help.
BTW I read that you do not have a RO/DI unit. Are you using tap or getting your r/O from somewhere? If you are using tap then I would look around and see if you can get r/o water from somewhere. That will help a lot. My lfs sells it fairly cheaply, but you have to bring in your own containers. Also, I have heard of people buying it from the grocery store. Do a search (on RS) for waterchanges or r/o and you should find the thread(s) I am talking about that tell you where everybody gets their water. There are many choices.
Again hope this helps. I have been there so I know exactly how you feel. mine was caused by some lr I bought on-line that was sold as cured but obviously was not or was not cured enough since it sent my system into a major cycle. unfortunately, I lost a number of fish before I was able to get things under control. Hope you have better luck.