It depends on the algae. Scale (cyano), some types of hair, and diatoms use phosphates and silicates.
1) Switch to HI-S RO/DI, initially the cost is higher than a phosphate removing resin but in the long run it will be cheaper.
2) Chaeto can eat phosphates as well. Run a separate refugium with chaeto in it. Use the water that has already been filtered to feed the refugium. Then run the drain from the refugium back through the filter. Prune the chaeto as necessary. Run the refugium on an off cycle. When the light is off on your display have it on in the refugium). If you have a problem with dirty chaeto then you are pumping dirty water into the refugium and not doing the 10 minutes every 2 weeks for maintaining it. You can also get some good macro algae that looks nice in a tank (coraline and others) that can eat the nutrients and won't overcrowd it.
3) Check your salt mixture. Cheaper salts can actually contain phosphates and silicates. A nice synthetic blend of SW can go a long way.
4) Add cleaners specific to the algae. emerald crabs, turbo snails, astrea snails, zebra hermits, dwarf blue hermits, and scarlet hermits can be matched to your type of algae. There are many more but some of the cleaners may not like a small tank. The ones I listed will be happy in a nano.
Also, if you plan on having light loving corals or anemones then lessening the light will starve out the zooanthelles. Without enough light will notice that your anemones are losing color, maybe even turning transparent. A sure sign that the zooanthelles aren't happy.