How can I reduce phosphates in RODI H20, Nitrates in tank, and Green Algae Spurts?

[edmund36]

I use RODI H2O for my 125 gallon combination fish and coral saltwater tank. I have 125 lb live rock and live sand inside. I test the TDS of the H2O that I just make (prior to mixing salt) and get a TDS reading of zero; however the measured Phosphate reading is at 0.5. Additionally my Nitrate reading continues to read about 10-15; never dropping lower. I have been using Phosphate absorbing media bag that I place in the sump where there is high water flow. I also have flourishing green algae that seems to grow wild within a week to two. This requires aggressive and time consuming brushing of live rock and cleaning sand bed and performing weekly 15 – 25% water changes.

I also can't understand why I have Phosphate with a Zero TDS reading?

Does anyone have any suggestions on fixing any of my key issues to get my phosphates down, nitrate lower, and reduce green algae spurts?

Any information would be greatly appreciated.

[DrHank]

Have you calibrated your TDS meter? That would be the first thing I'd check.

[mps9506]

Your ro/di water is measuring high in nitrates or your tank water?
Are you using kalkwasser for top off or just straight ro/di?

[prow]

after calibrating everything a couple other things comes to mind. one do you have a skimmer and/or growing macros? if not get both and make sure to get a good skimmer, dont go cheap on this one. ask questions before you buy.
i am thinking this is a new system and your rock was not fully cured. lots of die off maybe. it also sounds to me like your salt could be the source of your nitrates and phosphates. it could also be your mixing buckets leaching or a combo. what salt mix are you using and what are you mixing it in?
your going to need to test things to find out the root cause. test your fresh mixed salt. if + then clean your mixing bucket out with vinagar, soak for a few hours and then rinse well with RO/DI and mix a new batch salt water to see if its the salt or the mixing bucket.
if after all that you still have not found the cause, monitor your feeding so you dont feed to much at one time, try to kinda target feed the fish, only little bits at a time so most gets eaten before it get stuck in some rock crevice start to decompose. cut back on feeding if needed.
if its the rock, nothing you can do but water changes, phos media, carbon, good flow and heavy wet skimming. a reduction in lighting till the water parameters are all good. reducing your photoperiod will help keep the algae growth in check untill you get the water parameter all good. do you have any pics of you system. also how much flow do you have, gph wise total and the total water volume?