If fish are not present, lanthanum may be fine.
Other choices are:
1. Revises your target and do nothing. Some great tanks have 1+ ppm phosphate (see link below for example), and you may see no benefit from lowering it.
2. GFO. Expensive and binds trace elements.
3. Some sort of algae method (refugium, ATS, etc.). Removes trace elements
4. Aluminum oxide. Binds trace elements and releases aluminum.
This has more:
https://www.reef2reef.com/ams/randy’s-thoughts-on-nutrient-target-ranges.1087/
from it:
4. What targets seem reasonable? Of course, that depends on all the other factors at play, such as types of corals, availability of ammonia, particulate foods, etc. However, for a mature mixed reef, this would be how I personally would run it:
- Let nitrate float between 5 ppm and 50 ppm. I’d use gentle export in this range, such as growing macroalgae.
- Above 50 ppm, I’d begin to focus more on reducing it, by organic carbon dosing, turf or macroalgae, etc.
- Below 5 ppm, I’d begin to dose ammonia or feed more. The target level might drop lower if dosing ammonia, just like the heavy in/heavy out scenario where nitrate may not be as needed.
- Let phosphate float between about 0.06 ppm and 0.3 ppm. This range is higher than I’ve recommended in the past. I’d use gentle export in this range, such as growing macroalgae.
- Above about 0.3 ppm, I’d begin to focus more on reducing it, by turf or macroalgae, or a binder such as GFO or lanthanum (has its own risks to tangs). If a binder: GO SLOW. Turf and macroalgae will typically be slow enough.
- Below 0.06 ppm, I’d begin to dose sodium phosphate or feed more to get the level up.
