Hi Emma,
I don't think your issues are completely nutrient related, but having said that I think it would be advisable to switch to a fertiliser that contains nitrate and phosphate.
I'm curious as to why you're getting nitrate readings in the 50's, I'm from the North West and the nitrates in our tap water are usually fairly low, so that leads to believe that you either don't change much of the tank water every week, or your nitrate test results are skewed.
Most of the deficiencies you list are generally caused by insufficient levels of co2, rectifying this is the tricky part. If the tank is low tech then the main weapons to combat this would be to ensure good water flow around the tank and reducing the plants demand for co2 by limiting the amount of light they receive.
I'm going to make some assumptions about your tank, if these are wrong then please correct me.
From your description and photo in another thread I'm guessing you have a stock fluval vicenza 180l, if that's the case then you have a couple of issues, the first one is the standard 206/7 filter it comes with, even with its rated pump power of 780l/h its probably not going to be enough to circulate enough water around your tank, the actual circulation rate of the filter will be far less than 780l/h.
The second issue with the vicenza is the outlet position, the through tank positioning of that outlet, combined with twin outlet heads make it difficult to get good flow to all areas of the tank and plants.
The best but by no means perfect set up with that outlet was to have the duckbill at the back of the tank pointing straight down the length of the tank, almost parallel and pointing slightly upwards, and the duckbill nearest the front pointing towards the front glass but aiming about a third of the way down the length of the tank and pointing slightly down. Basically you will have to experiment a bit to try and get some movement in all your plants.
It's difficult to tell from the picture in your other post but it looks like the outlet is sat quite low in the water, if you can raise it a bit it will help a bit with getting a more circular flow and getting better gas exchange via surface movement. This is the height of my outlet.
If buying a bigger filter isn't an option then maybe consider getting a circulation pump or wavemaker to add extra flow to the tank.
Lastly do you have the ability to reduce the lighting intensity with the light it comes with? If so it might be an idea to reduce it a tad whilst you sort out the other things.
Hope that helps.