Hy guys! Today I did some tests on my aquarium water, and the results were as follows :
PH - 8, KH - 16, GH - 16, NO3- about 25. What do you think about this? I have a reverse osmosis system that I have not used it yet and I want to ask you whether it is sufficient to lower and maintain lower values ​​than those listed above. I have a tank of 90 L with 1X longfin albino female bn, 1x albino male bn, 1x longfin common bn female, 1x longfin bn male, and 3 bristlenoses which I don't know but I think they are ancistrus hoplogenys (not sure). I will try to take some pictures but afetr new year because i'm leaving in a small hollyday. I would like to specify that the substrate is 5-8 mm gravel and the tank is full of bogwood. I would love to hear also your advice and / or critics!!
All the best!!!

are the KH and GH in degrees?

Either way, the RO system will solve all your issues

your NO3 at 25 is acceptable but I personally like to keep it at or below 10 in all my tank but my African cichlids..they are to overstocked to keep them below 15 for aggression reasons. Just remember anything over 40 is toxic to your fish. And the lower the number the better it is for your fish and there health.

Yes Doug the kh and gh are in degrees. So it means i'm gonna start to use my RO system. Thank you guys!!!

Hello guys!!! I think I need some more advices but now regarding the water change. I just installed my RO system and the RO water properties are : PH - 6 degrees, KH - 2 degrees, GH - 1 degree. My question is...how is best to do the water change first with the new water. I intend to combine the ro water with tapwater and this combined water to drop it in the aquarium but I don't know how much of this water to put in my aquarium. Thank you guys and a Happy new year as this is my first post this year!!!

That is an excellent question.

Given that the pH difference is quite large (as you would expect) its not advisable to do a massive water change. In general fish can deal with a pH swing of 0.2~ without feeling stressed, indeed most planted tanks will change that much over the course of a day.

What I would do is make up a few mixtures of water in some containers. straight RO, 2:1 RO:tap/waste, 3:1, 5:1, 10:1 and leave them for 24 hours. Then teat the pH of them (this is to make sure that the disolved CO2 in the water is not affecting the reading). Then use the misture that fits the pH you are after. Generally the pH you are after with american fish is 6.8ish and the hardness should be about right too.

from there I would do some 20% water changes every couple of days until the water in your tank is settling down to the better pH, it will tank time and there might be a few odd swings but as long as you do it slowly it will come down.

Also, just as a mention, if your substrate is active at all (has the ability to leach or absorb chemicals) then this trasition will take a lot longer as the substrate will leach things back into the water that have been held in place by the high hardness of the water. That is why i switched substrate when i switched to RO water. I had huge levels of Phosphate leaching from my gravel, so i tossed it and got inert silica sand

Ok..Look what I did...First I mixed 1l of RO water with 1l of tapwater and the results was : ph about 8 degr, gh and kh 10 degr each but I did not liked the value of the ph. Then I mixed 250 ml of tapwater with 750 ml of RO water, results : ph about 7, kh 7 degr, gh 6 degr and NO3 about 25 mg/l. The values of the RO water from my system are : Ph about 6, kh 2, gh 0-1. As my aquarium ph is about 8 I thought that I can change about 50% from my aquarium water but I'm not very sure. I would like to mention that I do not have any plants yet, only boogwod and 1 coconut and I don't use CO2. What do you think? By the way thanks for the previous answer!!

Sounds like about a 1:4 ratio would give you the desired pH however, I would test them again after 24hrs as this will allow the CO2 to bubble out of solution, you can speed this up by adding an airstone to the water.

Once you are sure of your ratio that you want to use then I seriously recommend doing the transition slowly as not to shock your fish. The shift in water parameters will be huge and IMO more than enough to kill your fish if done too quickly.

I would stick to 20% changes every other day until the pH stabilises.

I agree with Doug.
Whatever I do to the water, I always let it "rest" for a day. Before adding to my tank, always checking the parametres.
This is the way I could avoid any water related stress.

Thank you for the advices!! As my RO system is working very but very slow I will try to do other test tomorow after 24 hours to see the result. As usual you were very helpful!! Thank you again and I will keep you informed about everything that happens!!! Cheers!!

RO systems are slow.

Mine drips, doesnt flow. That is the way it is meant to opperate. You can get faster flowing ones but they are more expensive and often require higher pressure.

Mine did 30 liters in a day and a half. Still waiting to fill 60 liter drum. The problem is that osmosis system is connected to the outlet of the shower and I need to disconnect the system always to take a shower and the drum is in the tub. Nice not? ...Today I intend to re arange my aquarium because of the brown water from it. Yesterday I forgot to ask you about the values of the kh 7 and gh 6. What do you think? It is ok for my long fins, comons and albinos? Thank you again for your answer!!! Cheers!!

I do not believe that those hardness levels would cause any problem.
BNs are often kept with Paracheirodon innesis, which are commonly known to prefer low KH and GH.
But let's see what other think of this, since this is my experience, only.

yeah, those water parameters are fine.

The issue with the RO system might be the input pressure. See if you can attach it to a different water point.

I had to reduce the input pressue on mine from about 1000 kpa to 400 kpa.

After more than 24 hours I made new tests as follows. RO/Tap water 1:4 : Ph-7.5, Gh-5 degr, Kh-6 degr, NO3 - betwen 12-25 mg/l. As my ph in the aquarium is 8 I think I can make a big change of the water because the diference of the ph is 0.5. What do you think. I'm not so happy with the value of the ph because I want it much lower. Do you think that the catapa is ok to lower the ph or you sugest anything else??? The values of the gh and kh are still ok for my bristlenoses??? Cheers!!