ALright,I have 20G planted tank and for two weeks now Im having a problem of high phosphate after huge water change of 75%. I made a test after 24 hours and it was very high .My test kit is 1 to 5ppm range and surprisingly, the color test came out a little bit darker than 5ppm color chart! This doesnt happens in the past.

Just last PWC, I took out from my aquarium one small wood branch that I suspect responsible for leaching phosphate, and again did 75%. After 24 hours the Phosphate is off the chart again. This is happening for 2 weeks now. Weeks prior to this, I have 15 neon tetras that slowly decrease in numbers to about 8 but I couldnt find the dead neons due to heavy plants. I have a feeling this is the cause of high phosphate.

I dont have algae in my tank except for some very few that are growing on the tip of my hairgrass. with very high Phosphate Im a little worried taht algae will soon take over my tank.

can anyone share how to control my phosphate level before algae start to show up?
Thanks!

Is the phosphate also in your tap water? Test some other water with your test kit that you know isn't high phosphate....it could be faulty. Test kits are really unreliable. I just had to throw out a nitrate test kit when it gave me three totally different readings on the same water.

High phosphate won't necessarily cause algae. I dose lots of phosphate in my tanks, I don't have a test kit so I just add what amounts to probably too much, plus whatever is in my tank/tap water besides that, and I've never been able to induce algae that way.

First, you need to calibrate the phosphate test kit with solutions having known amount of phosphate in them. Otherwise, you can't know if it is a test kit problem (very likely) or a problem with some rocks or substrate leaching phosphate into the water (not very likely), or a tap water problem.

If you search for it, there is at least one post on the forum telling how to make known phosphate concentration solutions, and how to use them.

There was no Phosphate leaching in my rocks and substrate neither in my tap water. I did test after I was surprised for the result that after 75%, in almost just 24 hours!, i have way off chart Phosphate result. This is not a reocurrence problem but the very first time in my 2 year old planted tank.

But thats a good advice to check the test kit. At least, It eases me with my worries of high PO4 in my tank.

Thanks for the info!

I would rather post this question here than making another thread., so...what PO4 test kit everybody is using here?

It doesn't really matter in that you still need to calibrate the kit, whether it is one people use a lot, or one no one uses. I don't test for phosphate at all, so I have no idea which is the best kit.

Ive read this before from the other forum sites but its been a week now I just could not find it.

Sometime things shows up when you dont need them. But when time comes that you need them the most they dont show.

Thanks for your advices anyway.

I can't find that post either

Maybe who ever wrote can remember where it is?

Do you use activated carbon in this tank? Only reason I ask is some low grade activated carbon brands us phosphoric acid in the activation/washing process.