Right, if your salinity is not the problem (which it very likely can be), lets sort out the slime!!:]
Firstly, do you have a proper reactor for GFH / GFO, in other words, one which fluidizes the media? If not, get one, you can pick up a cheap one from Sams, I think the boyu ones are around R400. Ensure you have enough GFH, 1ml of gfh per litre of tank water. Good brands are ROWA (if you can get, think I saw at Sams) or ATI or ORCA.
Get a reactor up and running.
Next: ORCA biocubes, at 2ml per litre of tank water. Again, are they being run as recommended by the manufacturer, it doesnt seem so from your sump pic?
Get an airpump and airstone the size of a R5 coin or thereabouts, pump rating of anything around 3 l per minute of airflow will suffice. Shouldnt set you back more than R150 Max!
Do you still have the original bag that came with the cubes? Read up on the bomb method and install the cubes accordingly.
If you dont have any cubes, they should be on Cpt shelves soon, I know aquapet have distributed pricelists to stores... Alternatively, try Jungle Aquatics for shipping....
You'll also need Liquid phos remover, Find some Phosphat E from brightwell or Caribsea Phosbuster Pro. If you cant find, contact me via PM.
Other than a bit of salt and water, the above should almost cover your costs of sorting out this
PO4 
problem.
If you needed to add more ORCA cubes, wait a week before you commence with the following.
Once you have the above up and running, its time to start the physical process:
You will need:
Alk test kits and alk supplement.
Scrubbing brush
A spare skimmer and a powerhead.
1 drum, about 60 Litres
1Drum about 100 litres to mix saltwater, more than one drum will be fine if too large.
4 buckets of about 25 Litre each.
Mix up enough salt and
RO to make 100 litres of water to a salinity of 35ppt,
SG of 1.026. Aerate for at LEAST three hours.
Siphon into the four 25L buckets about 10 litres of tankwater each.
Don't siphon from sandbed, siphon from midwater, Split this water into four of the 25 L buckets, each having about 15 litre in.
Replace the water into tank with freshly mixed water.The remaining water needs to go into your 60L drum with your spare skimmer and powerhead.
Now, take out pieces of liverock, and piece by piece, dunk a few times and shake vigorously in bucket one. Then scrub and repeat in bucket two. Place in the 60L drum.
Do about a quarter of your LR in buckets one and two and another quarter in buckets three and four.
Keep this drum in as dark a place as possible.
On a every second day basis, drip in the liquid
PO4 remover, quantity as recommended by manufacturer. You can also drip in some liquid
PO4 remover into your tank, clean filter sock every second day. Keep a close eye on alk levels and maintain if needed.
Cover your tank glass with newspaper and switch of the lights. Leave it like this for a week.
Return the rock to your tank, still keeping glass covered and do the same excersize with the remaining rock.
After one week contact me via PM or call zero eight three seven doublezero seven onedubble four to remind me to advise further.
